Pain

Pain

Definition and classification

Pain is a universal human experience. The International Association for the Study of Pain (IASP) defines pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage." Pain may be a symptom of an underlying disease or disorder, or a disorder in its own right.

At the same time that pain is a universal experience, however, it is also a complex one. While the physical sensations involved in pain may be constant throughout history, the ways in which humans express and treat pain are shaped by their respective cultures and societies. Since the 1980s, research in the neurobiology of pain has been accompanied by studies of the psychological and sociocultural factors that influence people's experience of pain, their use of health care systems, and their compliance with various treatments for pain. As of 2003, the World Health Organization (WHO) emphasizes the importance of an interdisciplinary approach to pain treatment that takes this complexity into account.

Types of pain

Pain can be classified as either acute or chronic. Acute pain is a direct biological response to disease, inflammation, or tissue damage, and usually lasts less than one month. It may be either continuous or recurrent (e.g., sickle cell disease). Acute pain serves the long-term wellbeing of humans and the higher animals by alerting them to an injury or condition that needs treatment. In humans, acute pain is often accompanied by anxiety and emotional distress; however, its cause can usually be successfully diagnosed and treated. Some researchers use the term "eudynia" to refer to acute pain.

In contrast, chronic pain has no useful biological function. It can be defined broadly as pain that lasts longer than a month following the healing of a tissue injury; pain that recurs or persists over a period of three months or longer; or pain related to a tissue injury that is expected to continue or get worse. Chronic pain may be either continuous or intermittent; in either case, however, it frequently leads to weight loss, sleep disturbances, fatigue , and other symptoms of depression . According to an article in the New York Times, chronic pain is the most common under-lying cause of suicide. Unlike acute pain, chronic pain is resistant to most medical treatments. It is sometimes called "maldynia," and is considered a disorder in its own right.

Pain that is caused by organic diseases and disorders is known as somatogenic pain. Somatogenic pain in turn can be subdivided into nociceptive pain and neuropathic pain. Nociceptive pain occurs when pain-sensitive nerve endings called nociceptors are activated or stimulated. Most nociceptors in the human body are located in the skin, joints and muscles, and the walls of internal organs. There may be as many as 1,300 nociceptors in a square inch (6.4 square centimeter) of skin. However, there are fewer nociceptors in muscle tissue and the internal organs, as they are covered and protected by the skin. Nociceptors are specialized to detect different types of painful stimuli—some are sensitive to heat or cold, while others detect pressure, toxic substances, sharp blows, or inflammation caused by infection or overuse.

In contrast to nociceptive pain, neuropathic pain results from damage to or malfunctioning of the nervous system itself. It may involve the central nervous system (the brain and spinal cord); the peripheral nervous system (the nerve trunks leading away from the spine to the limbs, plus the 12 pairs of cranial nerves on the lower surface of the brain); or both. Neuropathic pain is usually associated with an identifiable disorder such as stroke , diabetes, or spinal cord injury , and is frequently described as having a "hot" or burning quality.

Psychogenic pain is distinguished from somatogenic pain by the influence of psychological factors on the intensity of the patient's pain or degree of disability. The patient is genuinely experiencing pain—that is, he or she is not malingering—but the pain has either no organic explanation or else a weak one. Common psychogenic pain syndromes include chronic headache or low back pain ; atypical facial pain; or pelvic pain of unknown origin.

Some cases of psychogenic pain belong to a group of mental disorders known as somatoform disorders. According to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), somatoform disorders are defined by "the presence of physical symptoms that suggest a general medical condition," but cannot be fully explained by such a condition, by the direct effects of a drug or other substance, or by another mental disorder. The somatoform disorders include somatization disorder, characterized by chronic complaints of unexplained physical symptoms, often involving multiple sites in the body; hypochondriasis is a preoccupation with illness that persists in spite of the doctor's reassurance; and pain disorder, characterized by physical pain that is intensified by psychological factors, often becoming the focus of the patient's life and impairing his or her family relationships and ability to work.

It is important to recognize that some pain syndromes may involve more than one type of pain. For example, a cancer patient may suffer from neuropathic pain as a side effect of cancer treatment as well as nociceptive pain associated with pressure from the tumor itself on nociceptors in a blood vessel or hollow organ. In addition to the somatogenic pain, the patient may experience psychogenic pain related to the loss of physical functioning or attractiveness, coupled with anxiety about the progression or recurrence of the cancer. Other pain syndromes do not fit neatly into either somatogenic or psychogenic categories. A case in point would be certain types of chronic headache that involve the stimulation of nociceptors in the tissues of the head and neck as well as psychogenic factors related to the patient's handling of stress.

Description

How the body feels pain

A person begins to feel pain when nociceptors in the skin, muscles, or internal organs detect pressure, inflammation, a toxic substance, or another harmful stimulus. The pain message travels along peripheral nerve fibers in the form of electrical impulses until it reaches the spinal cord. At this point, the pain message is filtered by specialized nerve cells that act as gatekeepers. Depending on the cause and severity of the pain, the nerve cells in the spinal cord may either activate motor nerves, which govern the ability to move away from the painful stimulus; block out the painful message; or release chemicals that increase or lower the strength of the original pain message on its way to the brain. The part of the spinal cord that receives and "processes" the pain messages from the peripheral nerves is known as the dorsal horn.

After the pain message reaches the brain, it is relayed to an egg-shaped central structure called the thalamus, which transmits the information to three specialized areas within the brain: the somatosensory cortex, which interprets physical sensations; the limbic system, which forms a border around the brain stem and governs emotional responses to physical stimuli; and the frontal cortex, which handles thinking. The activation of these three regions explains why human perception of pain is a complex combination of sensation, emotional arousal, and conscious thought.

In addition to receiving and interpreting pain signals, the brain responds to pain by activating parts of the nervous system that send additional blood to the injured part of the body or that release natural pain-relieving chemicals, including serotonin, endorphins, and enkephalins.

Factors that affect pain perception

LOCATION AND SEVERITY OF PAIN Pain varies in intensity and quality. It may be mild, moderate, or severe. In terms of quality, it may vary from a dull ache to sharp, piercing, burning, pulsating, tingling, or throbbing sensations; for example, the pain from jabbing one's finger on a needle feels different from the pain of touching a hot iron, even though both injuries involve the same part of the body. If the pain is severe, the nerve cells in the dorsal horn transmit the pain message rapidly; if the pain is relatively mild, the pain signals are transmitted along a different set of nerve fibers at a slower rate.

The location of the pain often affects a person's emotional and cognitive response, in that pain related to the head or other vital organs is usually more disturbing than pain of equal severity in a toe or finger.

GENDER Recent research has shown that sex hormones in mammals affect the level of tolerance for pain. The male sex hormone, testosterone, appears to raise the pain threshold in experimental animals, while the female hormone, estrogen, appears to increase the animal's recognition of pain. Humans, however, are influenced by their personal histories and cultures as well as by body chemistry. Studies of adult volunteers indicate that women tend to recover from pain more quickly than men, cope more effectively with it, and are less likely to allow pain to control their lives. One explanation of this difference comes from research with a group of analgesics known as kappa-opioids, which work better in women than in men. Some researchers think that female sex hormones may increase the effectiveness of some analgesic medications, while male sex hormones may make them less effective. In addition, women appear to be less sensitive to pain when their estrogen and progesterone levels are high, as happens during pregnancy and certain phases of the menstrual cycle. It has been noted, for example, that women with irritable bowel syndrome (IBS) often experience greater pain from the disorder during their periods.

FAMILY Another factor that influences pain perception in humans is family upbringing. Some parents comfort children who are hurting, while others ignore or even punish them for crying or expressing pain. Some families allow female members to express pain but expect males to "keep a stiff upper lip." People who suffer from chronic pain as adults may be helped by recalling their family's spoken and unspoken "messages" about pain, and working to consciously change those messages.

CULTURE AND ETHNICITY In addition to the nuclear family, a person's cultural or ethnic background can shape his or her perception of pain. People who have been exposed through their education to Western explanations of and treatments for pain may seek mainstream medical treatment more readily than those who have been taught to regard hospitals as places to die. On the other hand, Western medicine has been slower than Eastern and Native American systems of healing to recognize the importance of emotions and spirituality in treating pain. The recent upsurge of interest in alternative medicine in the United States is one reflection of dissatisfaction with a one-dimensional "scientific" approach to pain.

There are also differences among various ethnic groups within Western societies regarding ways of coping with pain. One study of African American, Irish, Italian, Jewish, and Puerto Rican patients being treated for chronic facial pain found differences among the groups in the intensity of emotional reactions to the pain and the extent to which the pain was allowed to interfere with daily functioning. However, much more work on larger patient samples is needed to understand the many ways in which culture and society affect people's perception of and responses to pain.

Demographics

Acute pain, particularly in its milder forms, is a commonplace experience in the general population; most people can think of at least one occasion in the past week or month when they had a brief tension headache, felt a little muscle soreness, cut themselves while shaving, or had a similar minor injury. On the other hand, chronic pain is more widespread than is generally thought; the American Chronic Pain Association estimates that 86 million people in the United States suffer from and are partially disabled by chronic pain. Two Canadian researchers evaluating a set of 13 studies of chronic pain done in North America, Europe, and Australia reported that the prevalence of severe chronic pain in these parts of the world is about 8% in children and 11% in adults. In terms of the economic impact of chronic pain, various productivity audits of the American workforce have stated that such pain syndromes as arthritis, lower back pain, and headache cost the United States between $80 and $90 billion every year.

The demographics of chronic pain depend on the specific disorder, including:

Chronic pelvic pain (CPP) is more common in women than in men; it is thought to affect about 14% of adult women worldwide. In the United States, CPP is most common among women of reproductive age, particularly those between the ages of 26 and 30. It appears to be more common among African Americans than among Caucasians or Asian Americans. In addition, a history of sexual abuse before age 15 is a risk factor for CPP in adult life.

Lower back pain (LBP) is the most common chronic disability in persons younger than 45. One researcher estimates that 80% of people in the United States will experience an episode of LBP at some point in life. About 3–4% of adults are disabled temporarily each year by LBP, with another 1% of the working-age population disabled completely and permanently. While 95% of patients with LBP recover within six to 12 weeks, the back pain becomes a chronic syndrome in the remaining 5%.

Headaches in general are very common in the adult population in North America; about 95% of women and 90% of men in the United States and Canada have had at least one headache in the past twelve months. Most of these are tension headaches. Migraine headaches are less common than tension headaches, affecting about 11% of the population in the United States and 15% in Canada. Migraines occur most frequently in adults between the ages of 25 and 55; the gender ratio is about 3 F:1 M. Cluster headaches are the least common type of chronic headaches, affecting about 0.4% of adult males in the United States and 0.08% of adult females. The gender ratio is 7.5–5 M:1 F.

Atypical facial pain is a less-common chronic pain syndrome, affecting one or two persons per 100,000 population each year. It is almost entirely a disorder of adults. Atypical facial pain is thought to affect men and women equally, and to occur with equal frequency in all races and ethnic groups.

Evaluation of pain

Patient description and history

A doctor's first step in evaluating a patient's pain is obtaining a detailed description of the pain, including:

severity

timing (time of day; continuous or intermittent)

location in the body

quality (piercing, burning, aching, etc.)

factors that relieve the pain or make it worse (temperature or humidity; body position or level of activity; foods or medications; emotional stress, etc.)

its relationship to mood swings, anxiety, or depression

The doctor will then take the patient's medical history, including past illnesses, injuries, and operations as well as a family history. In some cases, the doctor may need to ask about experiences of emotional, physical, or sexual abuse. The doctor will also make a list of all the medications that the patient takes on a regular basis. Other information that may help the doctor evaluate the pain includes the patient's occupation and level of functioning at work; marriage and family relationships; social contacts and hobbies; and whether the patient is involved in a lawsuit for injury or seeking workers' compensation. This information may be helpful in understanding what the patient means by "pain" as well as what may have caused the pain, particularly because many people find it easier to discuss physical pain than anxiety, anger, depression, or sexual problems.

Some doctors may give the patient a brief written pain questionnaire to fill out in the office. There are a number of different instruments of this type, some of which are designed to measure pain associated with cancer, arthritis, HIV infection, or other specific diseases. Most of these rating questionnaires ask the patient to mark their pain level on a scale from zero to 10 or zero to 100 with zero representing "no pain" and the higher number representing "worst pain imaginable" or "unbearable pain." The patient then answers a few multiple-choice questions regarding the impact of the pain on his or her employment, relationships, and overall quality of life.

Physical examination

A thorough physical examination is essential in identifying the specific disorders or injuries that are causing the pain. The most important part of pain management is removing the underlying cause(s) whenever possible, even when there is a psychological component to the pain.

Special tests

Although there are no laboratory tests or imaging studies that can demonstrate the existence of pain as such or measure its intensity directly, the doctor may order special tests to help determine the cause(s) of the pain. These studies may include one or more of the following:

Imaging studies, usually x rays or magnetic resonance imagings (MRIs ). These studies can detect abnormalities in the structure of bones or joints, and differentiate between healthy and diseased tissues.

Electrodiagnostic tests. These tests include electromyography (EMG), nerve conduction studies, and evoked potential (EP) tests. In EMG, the doctor inserts thin needles in specific muscles and observes the electrical signals that are displayed on a screen. This test helps to pinpoint which muscles and nerves are affected by pain. Nerve conduction studies are done to determine whether specific nerves have been damaged. The doctor positions two sets of electrodes on the patient's skin over the muscles in the affected area. One set of electrodes stimulates the nerves supplying that muscle by delivering a mild electrical shock; the other set records the nerve's electrical signals on a machine. EP tests measure the speed of transmission of nerve impulses to the brain by using two electrodes, one attached to the patient's arm or leg and the other to the scalp.

Thermography. This is an imaging technique that uses infrared scanning devices to convert changes in skin temperature into electrical impulses that can be displayed as different colors on a computer monitor. Pain related to inflammation, nerve damage, or abnormalities in skin blood flow can be effectively evaluated by thermography.

Psychological tests. Such instruments as the Minnesota Multiphasic Personality Inventory (MMPI) may be helpful in assessing hypochondriasis and other personality traits related to psychogenic pain.

Treatment

Treatment of either acute or chronic pain may involve several different approaches to therapy.

Medications

Medications to relieve pain are known as analgesics. Aspirin and other nonsteroidal anti-inflammatory drugs, or NSAIDs, are commonly used analgesics. NSAIDs include such medications as ibuprofen (Motrin, Advil), ketoprofen (Orudis), diclofenac (Voltaren, Cataflam), naproxen (Aleve, Naprosyn), and nabumetone (Relafen). These medications are effective in treating mild or moderate pain. A newer group of NSAIDs, which are sometimes called "superaspirins" because they can be given in higher doses than aspirin without causing stomach upset or bleeding, are known as COX-2 inhibitors. The COX-2 inhibitors include celecoxib (Celebrex), rofecoxib (Vioxx), and valdecoxib (Bextra).

For more severe pain, the doctor may prescribe an NSAID combined with an opioid, usually codeine or hydrocodone. Opioids, which are also called narcotics, are strong painkillers derived either from the opium poppy Papaver somniferum or from synthetic compounds that have similar effects. Opioids include such drugs as codeine, fentanyl (Duragesic), hydromorphone (Dilaudid), meperidine (Demerol), morphine, oxycodone (OxyContin), and propoxyphene (Darvon). They are defined as Schedule II controlled substances by the Controlled Substances Act of 1970, which means that they have a high potential for abuse in addition to legitimate medical uses. A doctor must have a special license in order to prescribe opioids. In addition to the risk of abuse, opioids cause potentially serious side effects in some patients, including cognitive impairment (more common in the elderly), disorientation, constipation, nausea, heavy sweating, and skin rashes.

If the patient's pain is severe and persistent, the doctor will give separate dosages of opioids and NSAIDs in order to minimize the risk of side effects from high doses of aspirin or acetaminophen. In addition, the doctor may prescribe opioids that are stronger than codeine—usually morphine, fentanyl, or levorphanol.

The "WHO Ladder" for the treatment of cancer pain is based on the three levels of analgesic medication. Patients with mild pain from cancer are given nonopioid medications with or without an adjuvant (helping) medication. For example, the doctor may prescribe a tranquilizer to relieve the patient's anxiety as well as the pain medication. Patients on the second "step" of the ladder are given a milder opioid and a nonopioid analgesic with or without an adjuvant drug. Patients with severe cancer pain are given stronger opioids at higher dosage levels with or without an adjuvant drug.

Acute pain following surgery is usually managed with opioid medications, most commonly morphine sulfate (Astromorph, Duramorph) or meperidine (Demerol). In some cases, NSAIDs that are available in injectable form (such as ketorolac) are also used. Patient-controlled analgesia, or PCA, allows patients to control the timing and amount of pain medication they receive. Although there are oral forms of PCA, the most common form of administration involves an infusion pump that delivers a small dose of medication through an intravenous line when the patient pushes a button. The PCA pump is pre-programmed to deliver no more than an hourly maximum amount of the drug.

Some types of chronic pain are treated by injections in specific areas of the body rather than by drugs administered by mouth or intravenously. There are three basic categories of injections for pain management:

Joint injections. Joint injections are given to treat chronic pain associated with arthritis. The most common medications used are corticosteroids, which suppress inflammation in arthritic joints, and hyaluronic acid, which is a compound found in the joint fluid of healthy joints.

Soft tissue injections. These are given to reduce pain in trigger points (areas of muscle that are hypersensitive to touch) and bursae, which are small pouches or sacs containing tissue fluid that cushions pressure points between tendons and bones. When a bursa becomes inflamed—a condition called bursitis—the person experiences pain in the nearby joint. Corticosteroids are the drugs most often used in soft tissue injections, although the doctor may also inject an anesthetic into a trigger point in order to relax the muscle.

Nerve blocks. Nerve blocks are injections of anesthetic around the fibers of a nerve to prevent pain messages relayed along the nerve from reaching the brain. They may be used to relieve pain in specific parts of the body for a short period; a common example of this type of nerve block is the lidocaine injections given by dentists before drilling or extracting a tooth. Some nerve blocks are injected in or near the spinal column to control pain that affects a larger area of the body; an example is the epidural injection given to women in labor or to patients with sciatica . A third type of nerve block is administered to block the sympathetic nervous system as part of pain management in patients with complex chronic pain syndromes.

Surgery

Because surgery is itself a cause of pain, few surgical treatments to relieve pain were available prior to the discovery of safe general anesthetics in the mid-nineteenth century. For most of human history, doctors were limited to procedures that could be completed within two to three minutes because the patients could not bear the pain of the operation. Ancient Egyptian doctors gave their patients wine mixed with opium, while early European doctors made their patients drunk with brandy, tied them to the benches that served as operating tables, or put pressure on a nerve or artery to numb a specific part of the body.

Modern surgeons, however, can perform a variety of procedures to relieve either acute or chronic pain, depending on its cause. These procedures include:

removal of diseased or dead tissue to prevent infection

removal of cancerous tissue to prevent the spread of the cancer and relieve pressure on nearby healthy organs and tissues

correction or reconstruction of malformed or damaged bones

insertion of artificial joints or other body parts to replace damaged structures

organ transplantation

insertion of pacemakers and other electrical devices that improve the functioning of damaged organs or help to control pain directly

cutting or destroying damaged nerves to control neuropathic pain

PSYCHOTHERAPY Psychotherapy may be helpful to patients with chronic pain syndromes by exploring the connections between anger, depression, or anxiety and physical pain sensations. One type of psychotherapy that has been shown to be effective is cognitive restructuring, an approach that teaches people to "reframe" the problems in their lives—that is, to change their conscious attitudes and responses to these stressors. Some psychotherapists teach relaxation techniques, biofeedback, or other approaches to stress management as well as cognitive restructuring.

Another type of psychotherapy that is effective in treating some patients with chronic pain is hypnosis. Although there is some disagreement among researchers as to whether hypnosis works by distracting the patient's attention from painful sensations or whether it works by stimulating the release of endorphins (chemicals produced by the body that are released in response to stress or injury and act as natural analgesics), it has been approved by the American Medical Association since 1958 as a treatment for pain. Some therapists offer instruction in self-hypnosis to patients with chronic pain.

COMPLEMENTARY AND ALTERNATIVE (CAM) APPROACHES CAM therapies that are used in pain management include:

Acupuncture . Studies funded by the National Center for Complementary and Alternative Medicine (NCCAM) since 1998 have found that acupuncture is an effective treatment for chronic pain in many patients. It is thought that acupuncture works by stimulating the release of endorphins, the body's natural painkillers.

Yoga. Practiced under a doctor's supervision, yoga helps to maintain flexibility and range of motion in joints and muscles. The breathing exercises that are part of a yoga practice also relax the body.

Prayer and meditation. The act of prayer by itself helps many people to relax. In addition, prayer and meditation are ways to refocus one's attention and keep pain from becoming the center of one's life.

Naturopathy. Naturopaths include dietary advice and nutritional therapy in their treatment, which is effective for some patients suffering from chronic pain syndromes.

Hydrotherapy. Warm whirlpool baths ease muscular and joint pain.

Music therapy. Music therapy may involve listening to music, making music, or both. Some researchers think that music works to relieve pain by temporarily blocking the "gates" of pain in the dorsal horn of the spinal cord, while others believe that music stimulates the release of endorphins.

Pain management

Pain management refers to a set of skills and techniques for coping with chronic pain. The goal of pain management is not complete elimination of pain; rather, the patient learns to keep the pain at a level that he or she can tolerate, and to make the most of life in spite of the pain. The American Chronic Pain Association (ACPA) lists seven coping skills that help in managing pain:

not dwelling on physical pain symptoms

emphasizing abilities rather than disabilities

recognizing one's feelings about the pain and discussing them freely

using relaxation exercises to ease the emotional tension that makes pain worse.

doing mild stretching exercises every day (with medical approval)

setting realistic goals for improvement and evaluating them on a weekly basis

affirming one's basic rights: the right to make mistakes, the right to say no, and the right to ask questions

An important part of pain management is participation in a multidisciplinary pain program. Many hospitals and rehabilitation centers in the United States and Canada offer pain management programs. Ideally, the program will have its own unit apart from patient care areas. Good pain management programs offer comprehensive treatment that includes relaxation training and stress management techniques; group therapy, family therapy, personal counseling, and job retraining; physical therapy, including exercise and body mechanics; patient education regarding medications and other aspects of pain management; and aftercare or follow-up support.

The treatment team in a pain management program is usually headed by a neurologist , psychiatrist, or anesthesiologist with specialized training in pain management. Other members of the team include registered nurses, psychiatrists or psychologists, physical and occupational therapists, massage therapists, family therapists, and vocational counselors.

Clinical trials

As of December 2003, the National Institutes of Health (NIH) was sponsoring 35 studies related to various chronic pain conditions and the effectiveness of such treatments as acupuncture, hypnosis, yoga, COX-2 inhibitors, and several experimental drugs.

Special concerns

Pain management in special populations

Pain management in the elderly and in children poses additional challenges. Although 20% of adults over 65 take an analgesic on a regular basis, older people are more vulnerable to the drug's side effects, particularly the nausea and bleeding that sometimes results from long-term use of NSAIDs. Children require special attention because they do not have an adult's ability to describe their pain. New tools have been developed since the mid-1990s to measure pain in children and to help doctors understand their nonverbal cues.

Addiction and withdrawal

Doctors have debated the risk of opioid abuse for most of the past century. For many years, patients with severe chronic pain were not given enough of the drugs they needed to control their pain because of the fear that they would become addicted to the narcotics. In the mid-1980s, however, some experts in pain management argued that the risk of addiction was quite low, whether the patients suffered from cancer pain or from chronic pain unrelated to cancer. As a result, some synthetic narcotics—most notably oxycodone (OxyContin)—were widely prescribed and a growing number of patients became addicted to these drugs. As of 2003, researchers estimate that 3–14% of the population may have an underlying undiagnosed vulnerability to abuse these substances.

In addition to the risk of abuse, there is a risk of withdrawal symptoms and a temporary increase in pain (known as rebound pain) if opioid medications are dis-continued suddenly. Withdrawal symptoms include diarrhea, runny nose and watery eyes, restlessness, insomnia, anxiety, nausea, and abdominal cramps. These symptoms are usually treated with clonidine (Catapres), an antihypertensive drug, and NSAIDs or antihistamines. The various risks of long-term use of opioids in pain management are not yet fully understood.

Resources

BOOKS

Altman, Lawrence K., MD. Who Goes First? The Story of Self-Experimentation in Medicine. Berkeley, CA: University of California Press, 1998.

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Pain

The relief of pain and suffering has been a continuing human endeavor since the dawn of recorded history (see Keele 1957). Yet despite centuries of observation and study, we are only beginning to achieve an understanding of the subtleties and complexities of pain. Even though pharmacologists have provided effective “painkillers,” we know little about where and how these drugs act. Surgical procedures that are usually effective in relieving pain can sometimes produce dismal failures, often enough to convince us that we are far from understanding the neurological mechanisms that subserve pain perception.

Part of the difficulty of understanding pain mechanisms lies in the divergent empirical approaches to the problem. Sensory physiologists, anatomists, and psychologists (see Ruch & Fulton 1960, pp. 300-368) have studied pain as a sensory phenomenon and have tended to neglect its motivating aspects. Learning theorists (Miller 1951; Bindra 1959) have dealt with pain primarily as a drive producer and negative reinforcing agent but have generally ignored the other facets of the problem. Finally, medical clinicians, such as anesthetists (Beecher 1959) and surgeons (White & Sweet 1955), have regarded pain as indicative of tissue pathology that has to be treated and abolished and have often had to postulate hypothetical neural mechanisms to account for the complex phenomena they observe. These three approaches are so different that it is not surprising that “pain” has never been satisfactorily defined (Beecher 1959).

The major obstacle to understanding pain, however, has been the perpetuation of a number of theories that have had a powerful influence on the field. The persistence of these theories has resulted in heated controversies that have endured since the beginning of this century. Consequently, one of the most difficult tasks in this field is to separate fact from theory. For this reason the psychological and clinical phenomena of pain, which must be accounted for by any satisfactory theory, will be described before physiological theories and experiments are discussed.

The obvious biological significance of pain has led to the general belief that it must always occur after injury and that the intensity of pain perceived is proportional to the amount and extent of the damage. The positive aspect of pain is universally recognized: it warns us that something biologically harmful is happening. Reports (Sternbach 1963) of people who are born without the ability to feel pain provide convincing testimony to its value. Such a person sustains extensive burns and bruises during childhood and learns only with difficulty to avoid inflicting severe wounds on himself. Nevertheless, there is convincing evidence that pain, in higher species at least, is not simply a function of the amount of bodily damage alone. Rather, the amount and quality of pain perceived are also determined by past experience and attention, by the ability to understand the cause of the pain and to grasp its consequences. This fact, supported by a large body of evidence, presents a challenge to pain theorists.

Cultural factors

Cultural values are known to play an essential role in the way a person perceives and responds to pain. In Western culture, for example, childbirth is considered by many to be one of the worst pains a human being can experience. Yet the practice of couvade (Kroeber [1923] 1948, pp. 542-543) in cultures throughout the world indicates the extent to which culture contributes to the intensity of pain. In some of these cultures a woman who is going to have a baby continues to work until the child is about to be born. Her husband then gets into bed and groans as though he were in great pain while she bears the child. In more extreme cases, the husband stays in bed with the baby to recover from the terrible ordeal and the mother returns almost immediately to her household work. Dick-Read (1944) has stressed the great extent to which culturally determined fear enhances the amount of pain felt during labor and birth and points out how difficult it is to dispel such fear.

Role of anxiety

The effect of anxiety on the intensity of perceived pain is further demonstrated by studies on the effectiveness of placebos. Beecher found that severe pains (such as postsurgical pain) can be relieved in about 35 per cent of patients by giving them a placebo, such as sugar or saline solution, in place of morphine or other analgesic drugs. As Beecher has pointed out, only about 75 per cent of patients experiencing severe pain are satisfactorily relieved even when given large doses of morphine; the placebo effect thus accounts for about 50 per cent of the drug effectiveness (1959, p. 169). This in no way implies that people who are helped by a placebo do not have real pain; no one will deny the reality of postsurgical pain. Rather it illustrates the powerful contribution of anxiety to pain perception, since the physician may often relieve pain significantly by prescribing placebos to lower the patient’s anxiety as well as by treating the wounded areas of the body. Similarly, experiments by Hall and Stride (1954) have shown that the anticipation of pain raises the level of anxiety and, consequently, the intensity of perceived pain. Experiments by Hill and his associates (1952a; 1952b) have shown that a given level of electric shock or burning heat is perceived as significantly more painful when anxiety is experimentally induced than it is after anxiety has been dispelled. These studies also show that morphine diminishes pain if the anxiety level is high but has no demonstrable effect under conditions of low anxiety.

Role of attention

Attention to stimulation also contributes to pain intensity. It is frequently noted that contestants in a fight or in the heat of a game can receive severe wounds without being aware that they have been hurt. Indeed, almost any situation that attracts a sufficient degree of excited, prolonged attention may provide the conditions for other stimulation to go by unnoticed, including wounds that would cause considerable suffering under normal circumstances. Hypnosis, a trance state in which attention is focused intensely on a person or an object, is perhaps the best-known condition in which people can be cut or burned without their reporting any perception of the event (Barber 1959). Failure in attention may also account for the fact that dogs raised in sensory isolation in specially constructed cages from infancy to maturity (Melzack & Scott 1957) show a frequent failure to respond to normally painful stimulation, such as a flaming match or pinprick, after they are released from their cages. Since these dogs exhibit a remarkably high level of excitement, it is reasonable to suppose (Melzack & Burns 1963) that they fail to attend selectively to these noxious stimuli when they are presented in an unfamiliar environment in which all stimuli are equally attention-demanding. [SeeAttentionandHypnosis.]

Role of meaning

Finally, there is striking evidence to show that the meaning associated with a pain-producing situation is extremely important in determining the degree and quality of pain that are perceived. Beecher observed soldiers who were severely wounded in battle and found that only one out of three claimed that he had enough pain to require morphine. Most of the soldiers denied having pain from their wounds or had so little that they did not want medication to relieve it. In contrast, four out of five hospitalized civilians who had surgical incisions matching the wounds received by the soldiers claimed that they were in severe pain and demanded a morphine injection. Beecher concluded that in the wounded soldier, the response to injury was relief, thankfulness for his escape alive from the battlefield, even euphoria (his wound was a good thing); to the civilian, his major surgery, even though essential, was a depressing, calamitous event; there is no simple direct relationship between the wound per se and the pain experienced (1959, p. 165).

The importance of the meaning associated with a pain-producing situation is made especially clear in conditioning experiments by Pavlov (1923). He found that if electric shocks administered to a dog’s paw are followed consistently by the presentation of food, they eventually fail to elicit signs of pain and produce an entirely different response: the dog salivates, wags its tail, and turns toward the food dish. Masserman (1950) has carried these experiments still further. After cats had been taught to respond to electric shock as a signal for feeding, they were trained to administer the shock to themselves by walking up to a switch and closing it.

Theories of pain are satisfactory only to the extent that they are able to account for all of the relevant phenomena. There are many forms of pathological or clinical pain that present bizarre features that are difficult to explain; yet they must fit into the framework of pain theory. Two pain syndromes, phantom-limb pain and causalgia, have been studied in detail and represent the most terrible of human pain experiences.

Phantom-limb pain

The presence of a painless phantom limb is reported by the majority of amputees almost immediately after amputation. About 30 per cent, however, have the misfortune to develop pains in the phantom limb, and in about 5 per cent the pain is severe. These pains may be occasional or continuous, but they are felt in definite parts of the phantom limb (Livingston 1943; Feinstein et al. 1954). The pain tends to decrease and eventually disappear in most amputees. There are a few, however, in whom the pain increases in severity over the years and may even spread to other regions of the body, so that merely touching these new “trigger zones” will provoke spasms of severe pain in the phantom limb (Cronholm 1951). Unfortunately, the conventional surgical procedures for controlling pain usually fail to bring permanent relief; thus, these patients may undergo a series of such operations without any decrease in the severity of the pain (Livingston 1943). Phenomena such as these defy explanation in terms of our present physiological knowledge. Attempts have been made to label these unfortunate people as “neurotic” (see Kolb 1954), but there is convincing evidence that argues against such an explanation for all cases (Livingston 1943).

There are a number of features of phantomlimb pain that provide clues toward understanding the mechanisms underlying it.

Peripheral factors. It is known (Livingston 1943) that the neuromas (small nodules of regenerating nerve tissue) in the stumps of amputated patients contribute to phantom-limb pain, since pressure on them can trigger bouts of unbearable pain. Yet excision of neuromas or reamputation at a higher level usually fails to relieve pain for more than a few weeks or months (Livingston 1943; Cronholm 1951). Indeed there is almost unanimity of opinion that peripheral operations are likely to fail and that other procedures should be sought.

Role of sympathetic nervous system. The sympathetic nervous system also plays an important role, because cutting or temporarily anesthetizing the sympathetic ganglia entering the spinal cord (Livingston 1943) is capable of dramatically removing the pain for variable periods of time. Yet it is clearly not the sole cause of phantom-limb pain because pain often returns after the sympathetic ganglia are surgically removed. The contribution that the autonomic nervous system as a whole makes to phantom-limb pain is clear, moreover, from observations (Henderson & Smyth 1948) that pain is triggered in many patients at the start of urination or defecation. Similar sudden increases of pain may be triggered by sexual excitement and orgasm (Kolb 1954).

Emotional factors. Phantom-limb pain is greatly enhanced by emotional factors. Seeing a disturbing movie (Kolb 1954), having an argument with wife or husband (Livingston 1943), and other emotionally disturbing situations are capable of initiating or increasing the intensity of phantom-limb pain.

Role of sensory input. Either increasing or decreasing the sensory input from the stump or related areas is capable of providing relief from phantom-limb pain. Feinstein, Luce, and Langton (1954) have demonstrated that injection of the vertebral tissues of amputees with 6 per cent salt solution produces severe pain at the site of injection, which then radiates into the phantom limb. After this initial onset of pain, there is usually a decrease of the phantom-limb pain. Occasionally the pain vanishes completely following a single injection. Similarly dramatic results may occur after an injection of anesthetic procaine into the vertebral tissues in the attempt to decrease sensory input from these regions. Comparable findings are reported when stimulation is increased or decreased at the peripheral level. Injection of the tender neuromas of the stump with procaine solution often brings about sudden and dramatic relief for variable periods of time. On the other hand, stimulation of the stump, by massage or by hitting it with a small rubber mallet, often produces the only possible relief from phantom-limb pain in a large number of patients (Russell & Spalding 1950).

Spread of pain and trigger sites. Finally, there is the spread of pain and of trigger sites beyond the segments directly involved in the limb. Thus Cronholm (1951) found that touching the small of the back or the forehead may induce spasms of pain in a phantom leg. These trigger zones spread in unusual, seemingly random patterns and are not related in any apparent way to the segmental distribution of the somatic afferent nerves.

Causalgia

Causalgia is a severe, unremitting, burning pain that occurs in about 2 per cent of people who have sustained a peripheral-nerve injury. The pain is felt in the affected limb but may spread to other parts of the body. It exhibits many of the features of phantom-limb pain as well as other even more bizarre characteristics. Surgical procedures have only limited success in the treatment of causalgic pain. Section of the peripheral nerve at a higher level, amputation of the limb, and cutting the dorsal sensory roots that enter the spinal cord have all produced as many failures as successes. Indeed, operations have been performed for causalgic pain at nearly every possible site in the pathway from the peripheral receptors to the sensory cortex, and at every level the story is the same: some encouraging results but a disheartening tendency for the pain to return (see Livingston 1943).

Nonspecific triggering stimuli. A further remarkable feature of causalgia is that a variety of stimuli that can hardly be called “adequate pain stimuli” can produce increases in pain. Sudden noises, the sound of airplanes, the scraping of a shoe on the floor, emotional disturbances, almost any stimulus that elicits a startle response, touching the damaged leg or arm or even blowing lightly on it are all capable of making the pain worse (Livingston 1943).

Sympathetic nervous system in causalgia. The involvement of the sympathetic nervous system in causalgia, as in phantom-limb pain, is obvious. The skin becomes dry and cool, and sweat may drip from a single finger (Livingston 1943). Moreover, injection of anesthetic procaine into the sympathetic ganglia may dramatically abolish the pain for variable periods of time. But the fact that pain may return after surgical removal of sympathetic ganglia (Livingston 1943) indicates that sympathetic-nervous-system activity is not the primary cause of the pain.

Role of sensory input in causalgia. Similarly, an abnormal sensory input from the site of the nerve lesion is clearly implicated as an important cause of causalgic pain. Procaine blocks proximal or distal to the lesion may abolish pain for hours or days, and on rare occasions it never returns. Livingston (1943) reports, moreover, that the pain can be abolished if the patient is trained to tolerate sensory stimulation of the affected limb and is encouraged to use it normally. But the frequent failure of peripheral-nerve surgery to abolish pain indicates that more is involved than simply an irritating peripheral lesion.

The psychological and clinical phenomena of pain that have been described above must be taken into account in any satisfactory theory of pain. Since physiological evidence on the sensory mechanisms of pain is intimately bound up with the theories in vogue at the time, it is necessary to consider the physiology in terms of theoretical orientation.

Orthodox specificity theory

The orthodox theory of pain, still the most widely held, was first proposed by Max von Frey in 1895 (see Melzack & Wall 1962) and was subsequently extended in a vast literature on pain mechanisms (see Bishop 1946; White & Sweet 1955). Von Frey’s theory, also known as specificity theory, proposed that there are specific pain receptors (the free nerve endings) which, when stimulated, give rise to pain and only to pain. Following this idea, physiologists proposed that pain is carried by peripheral-nerve fibers of particular diameter (the A delta and C fibers), a distinct spinal-cord system (the spinothalamic tract), and a particular projection area in the thalamus, which is presumed to be the seat of pain sensation. Specificity theory has been the subject of heated debate and controversy since it was first proposed, and an attempt has recently been made (Melzack & Wall 1962) to analyze the features of this theory that make it both attractive and repugnant.

Von Frey’s specificity theory has three underlying assumptions. The first is physiological: the theory assumes that each receptor in the skin has a specific irritability, that is, a lowest threshold for some particular stimulus energy. There is convincing evidence to indicate that this assumption is valid, and it has been restated by Sherrington (1906) as the law of the adequate stimulus. The second assumption concerns the morphological receptor that is associated with pain experience. It is now certain (Weddell 1955) that the free nerve endings transmit information not only about pain but also about warmth, cold, touch, itch, tickle, and the myriad other experiences that derive from cutaneous stimulation. The third assumption of specificity theory is psychological: it assumes a one-to-one relation between skin receptor and psychological experience.

Inadequacy of specificity theory. It is the assumption of a one-to-one relation between skin receptor and psychological experience that has led to attempts at outright rejection of von Frey’s theory. The theory implies a direct transmission system in which there is an invariant, one-to-one relationship between stimulus intensity, peripheral receptor, central-nervous-system pathway, and intensity of pain perceived. Almost all of the psychological and clinical phenomena described above argue against this simple one-to-one relationship. The fact that a light puff of air on the skin, emotional disturbance, or arousal of the autonomic nervous system can elicit bouts of excruciating causalgic and phantom-limb pain indicates that there is more to pain mechanisms than a straight-through system from specific peripheral receptors to a pain center in the brain.

Pattern theory

Alternative theories have been proposed to replace specificity theory. Their history dates back to the time of von Frey’s theory, and each is characterized by complex physiological mechanisms that are postulated to account for the complex psychological and clinical phenomena of pain. Collectively, these alternative theories may be brought together under a single conceptual name: pattern theory. It proposes essentially that information at the skin is coded in the form of nerve-impulse patterns, which provide the basis of our sensory perceptions. These patterns, moreover, can undergo modification during their transmission centrally, that is, the quality and intensity of pain can be modulated by events in the central nervous system, such as memories, emotions, and attention. The most recent formulation of a pattern theory for cutaneous perceptions (Melzack & Wall 1962) proposes that skin receptors have specialized physiological properties for the transmission of particular kinds and ranges of stimuli into patterns of nerve impulses, rather than modality-specific information, and that every discriminably different somesthetic perception is produced by a unique pattern of nerve impulses.

The concept of patterning of nerve impulses, together with three recently discovered features of the skin sensory system, provides the basis for a new theory of pain (Melzack & Wall 1965). First, there is now abundant physiological and anatomical evidence of efferent fiber systems that run from the brain down to the afferent pathways and are capable of modifying or inhibiting the afferent pattern in the course of its transmission centrally (see Livingstone 1959). Second, the dorsal-column and dorsolateral systems of the spinal cord have properties (see Melzack & Wall 1965) indicating that their function may well be that of arousing the central processes subserving memories of prior experience, attention, and so forth, which are then able to act downward on the afferent impulse patterns.

The third line of evidence derives from the recent work of Wall (1962), which shows that a sensory input arriving at the spinal cord has two effects. First, it transmits information from the peripheral nerve to spinal-cord cells whose fibers go to the brain, and, second, it influences the properties of the substantia gelatinosa, a diffusely interconnected band of tissue lying throughout the length of the spinal cord in the dorsal horn. Mendell and Wall (1964) have shown that the substantia gelatinosa can both inhibit and facilitate the transmission of the coded sensory information from peripheral fiber to central cell. They point out that there is a continuous tonic input from the periphery to the substantia gelatinosa, so that continual inhibitory control is exerted over the transmission of nerve impulses across the synapses from peripheral fibers to central cells.

This tonic inhibition can be increased or decreased by the size of the fiber stimulated. Thus the largest A fibers increase the tonic inhibitory effect of the substantia gelatinosa, while the smalldiameter C fibers decrease the inhibitory influence, that is, actually facilitate the transmission of information in such a way that there is a greater likelihood of all inputs, from the peripheral and autonomic nervous systems, as well as from the brain, summating and thereby producing the characteristic pattern of high-frequency bursts of impulses that signals pain. The substantia gelatinosa,moreover, is a functionally continuous unit, so that different parts of the body are connected in a way that permits the spread of trigger zones observed in phantom-limb and causalgic pain.

Gate control theory

These three features of the skin sensory system provide the basis for a gate control theory of pain (Melzack & Wall 1965). The theory proposes that (1) the substantia gelatinosa functions as a gate control system that modulates the amount of input transmitted from the peripheral fibers to the dorsal horn transmission (T) cells; (2) the dorsal column and dorsolateral systems of the spinal cord act as a central control trigger, which activates selective brain processes that influence the modulating properties of the gate control system; and (3) the T cells activate neural mechanisms that constitute the action system responsible for both response and perception.

Figure 1 provides a schematic diagram of the gate control theory, showing the large-diameter and small-diameter peripheral fibers and their projections to the substantia gelatinosa (SG) and T cells in the dorsal horn. The inhibitory effect exerted by the substantia gelatinosa on the afferent fiber terminals is shown to be increased by activity in the large fibers and decreased by activity in the small fibers. The central control trigger is represented by the heavy line running from the largefiber system to the central control mechanisms; these mechanisms, in turn, project back to the gate control system. The T cells project to the entry cells

of the action system. Excitation is represented by +; inhibition by –.

The theory proposes that pain phenomena are determined by interactions among these three systems. For example, a marked loss of the large peripheral-nerve fibers, which may occur after traumatic peripheral-nerve lesions or in some of the neuropathies (Greenfield 1958), such as postherpetic neuralgia (Noordenbos 1959), would decrease the normal presynaptic inhibition of the input by the gate control system. Thus, the input arriving over the remaining large and small fibers is transmitted through the unchecked, open gate produced by the small-fiber input. This, together with the opportunity for summation of inputs into thesubstantia gelatinosa from other parts of the body and from the brain, provides the basis for the triggering of pain by a variety of stimuli that are normally not noxious.

Pain has generally been considered primarily a sensory experience somewhat similar to sight or hearing. In one important respect, however, pain differs from vision and hearing: it has a unique, distinctly unpleasant quality that wells up in consciousness and obliterates anything we may have been thinking or doing at the time. It becomes overwhelming and demands immediate attention. Besides its sensory component, then, pain also has a strong emotional quale that drives (or motivates) the organism into doing something about it. Ensuing responses are such as to stop the pain quickly by whatever course of action is possible.

Introspectionist psychologists at the turn of the century made a sharp distinction between the sensory and the affective dimensions of the pain experience. Titchener (1909) was convinced that there is a continuum of feeling in conscious experience, distinctly different from sensation, that ranges through all degrees of pleasantness and unpleasantness. These two dimensions, the sensory quality and the affective quale, are brought clearly into focus by clinical studies on prefrontal lobotomy (Freeman & Watts 1942), a neurosurgical operation for intense pain in which the connections between the prefrontal lobes and the rest of the brain are severed. Typically, these patients report after the operation that they still have pain but that it no longer bothers them; they simply no longer care about the pain and often forget it is there. It is certain that the operation does not stop pain perception entirely, since the sensory component is still present. The predominant effect of the operation seems to be on the affective coloring of the total pain experience; the terribly unpleasant quality of the pain has been abolished.

Brain areas involved. Recent experiments suggest that there are portions of the brain that are particularly concerned with the motivating aspects of behavior. Miller (1957) has recently found subcortical areas in the brain that produce vigorous escape reactions, cries, and other emotional behavior characteristic of pain perception when they are stimulated electrically. It seems possible that the activities in these areas provide the neural substrate for the affective, “driving” component of pain perception. [SeeNervous System, article onBrain Stimulation.]

In recent years the evidence on pain has moved in the direction of recognizing the plasticity and modifiability of events occurring in the central nervous system. In the lower part of the brain at least, the patterns of nerve impulses evoked by noxious stimulation travel over multiple pathways going to widespread regions of the brain and not along a single path going into a “pain center.” The psychological evidence lends strong support to the consideration of pain as a perception determined by the unique past history of the individual, by the meaning the stimulus has to him, by his “state of mind” at the moment, as well as by the sensory nerve patterns evoked by a physical cause. In this way, pain becomes a function of the whole individual, including even his thoughts and hopes for the future.

Pain, then, refers to a category of complex experiences, not to a kind of stimulation. Clearly, there are many varieties and qualities of experience that are simply categorized under the broad heading of pain because they defy more subtle verbal description. There are the pains of a scalded hand, a stomach ulcer, a sprained ankle; there are headaches and toothaches. But there is also the heartache of the scorned lover, the pain of losing a dear friend. It may be argued that the pain of bereavement is very different from the pain that follows surgery. But the pain of a coronary occlusion is just as uniquely different from the pain of a scalded hand.

Why is it so difficult to achieve a satisfactory definition of pain? The answer appears to be that pain is not a single, specific experience that can be analyzed and manipulated. It may be agreed that pain, like vision and hearing, is a complex perceptual experience. But the numerous, diverse causes of pain prevent the specification of a particular kind of environmental energy as the specific stimulus for pain, in the way that light can be specified as the adequate stimulus for vision, and air pressure waves for hearing. Pain is a category of experiences, signifying a multitude of different unique events having different causes and characterized by different qualities varying along a number of sensory and affective dimensions.

Dick-Read, Grantly (1944) 1959 Childbirth Without Fear. 2d ed., rev. New York: Harper. → A paperback edition was published in 1962 by Dell.

Feinstein, Bertram; Luce, James C.; and Langton, John N. K. 1954 The Influence of Phantom Limbs. Pages 79-138 in National Research Council, Advisory Committee on Artificial Limbs, Human Limbs and Their Substitutes. New York: McGraw-Hill.

Masserman, Jules H. 1950 A Biodynamic Psychoanalytic Approach to the Problems of Feeling and Emotion. Pages 40-75 in International Symposium on Feelings and Emotions, Second, Moose Heart, Illinois, 1948,Feelings and Emotions. New York: McGraw-Hill.

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Pain

Pain

Definition

Pain is an unpleasant feeling that is conveyed to the brain by sensory neurons. The discomfort signals actual or potential injury to the body. However, pain is more than a sensation, or the physical awareness of pain; it also includes perception, the subjective interpretation of the discomfort. Perception gives information on the pain's location, intensity, and something about its nature. The various conscious and unconscious responses to both sensations and perception, including the emotional response, add further definition to the overall concept of pain.

Description

Pain arises from any number of situations. Injury is a major cause, but pain may also arise from a wide variety of illnesses. It may accompany a psychological condition, such as depression , or may even occur in the absence of a recognizable trigger.

Acute pain

Acute pain often results from ordinary tissue damage, such as a skin burn or broken bone. Acute pain can also be associated with headaches or muscle cramps. This type of pain usually goes away as the injury heals or the cause of the pain (stimulus) is removed.

To understand acute pain, it is necessary to understand the nerves that support it. Nerve cells, or neurons, perform many functions in the body. Although their general purpose, providing an interface between the brain and the body, remains constant, their capabilities vary widely. Certain types of neurons are capable of transmitting a pain signal to the brain.

As a group, these pain-sensing neurons are called nociceptors, and virtually every surface and organ of the body is wired with them. The central part of these cells is located in the spine, and they send threadlike projections to every part of the body. Nociceptors are classified according to the stimulus that prompts them to transmit a pain signal. Thermoreceptive nociceptors are stimulated by temperatures that are potentially tissue damaging. Mechanoreceptive nociceptors respond to a pressure stimulus that may cause injury. Polymodal nociceptors are the most sensitive and can respond to temperature and pressure. Polymodal nociceptors also respond to chemicals released by the cells in the area from which the pain originates.

Nerve cell endings, or receptors, are at the front end of pain sensation. A stimulus at this part of the nociceptor unleashes a cascade of neurotransmitters (chemicals that transmit information within the nervous system) in the spine. Each neurotransmitter has a purpose. For example, substance P relays the pain message to nerves leading to the spinal cord and brain. These neurotransmitters may also stimulate nerves leading back to the site of the injury. This response prompts cells in the injured area to release chemicals that not only trigger an immune response, but also influence the intensity and duration of the pain.

Chronic and abnormal pain

Chronic pain refers to pain that persists after an acute injury heals, cancer pain, pain related to a persistent or degenerative disease, and long-term pain from an unidentifiable cause. It is estimated that one in three people in the United States will experience chronic pain at some point in their lives. Of these people, approximately 50 million are either partially or completely disabled.

Chronic pain may be caused by the body's response to acute pain. In the presence of continued stimulation of nociceptors, changes occur within the nervous system. Changes at the molecular level are dramatic and may include alterations in genetic transcription of neurotransmitters and receptors. These changes may also occur in the absence of an identifiable cause; one of the frustrating aspects of chronic pain is that the stimulus may be unknown. For example, the stimulus cannot be identified in as many as 85% of individuals suffering lower back pain.

Other types of abnormal pain include allodynia, hyperalgesia, and phantom limb pain. These types of pain often arise from some damage to the nervous system (neuropathic). Allodynia refers to a feeling of pain in response to a normally harmless stimulus. For example, some individuals who have suffered nerve damage as a result of viral infection experience unbearable pain from just the light weight of their clothing. Hyperalgesia is somewhat related to allodynia in that the response to a painful stimulus is extreme. In this case, a mild pain stimulus, such as a pin prick, causes a maximum pain response. Phantom limb pain occurs after a limb is amputated; although an individual may be missing the limb, the nervous system continues to perceive pain originating from the area.

Causes & symptoms

Pain is the most common symptom of injury and disease, and descriptions can range in intensity from a mere ache to unbearable agony. Nociceptors have the ability to convey information to the brain that indicates the location, nature, and intensity of the pain. For example, stepping on a nail sends an information-packed message to the brain: the foot has experienced a puncture wound that hurts a lot.

Pain perception also varies depending on the location of the pain. The kinds of stimuli that cause a pain response on the skin include pricking, cutting, crushing, burning, and freezing. These same stimuli would not generate much of a response in the intestine. Intestinal pain arises from stimuli such as swelling, inflammation, and distension.

Diagnosis

Pain is considered in conjunction with other symptoms and individual experiences. An observable injury, such as a broken bone, may be a clear indicator of the type of pain a person is suffering. Determining the specific cause of internal pain is more difficult. Other symptoms, such as fever or nausea , help narrow down the possibilities. In some cases, such as lower back pain, a specific cause may not be identifiable. Diagnosis of the disease causing a specific pain is further complicated by the fact that pain can be referred to (felt at) a skin site that does not seem to be connected to the site of the pain's origin. For example, pain arising from fluid accumulating at the base of the lung may be referred to the shoulder.

Since pain is a subjective experience, it may be very difficult to communicate its exact quality and intensity to other people. There are no diagnostic tests that can determine the quality or intensity of an individual's pain. Therefore, a medical examination will include a lot of questions about where the pain is located, its intensity, and its nature. Questions are also directed at what kinds of things increase or relieve the pain, how long it has lasted, and whether there are any variations in it. An individual may be asked to use a pain scale to describe the pain. One such scale assigns a number to the pain intensity. For example, 0 may indicate no pain, and 10 may indicate the worst pain the person could imagine. Scales are modified for infants and children to accommodate their level of comprehension.

Treatment

Both physical and psychological aspects of pain can be dealt with through alternative treatment. Some of the most popular treatment options include herbal therapies, nutritional therapies, homeopathy, acupressure and acupuncture , massage, chiropractic, guided imagery , and relaxation techniques, such as yoga , hypnosis, and meditation . Hydrotherapy can also be very beneficial for pain relief.

Herbal therapies

Mild natural painkillers are used as herbal remedies for pain. They should only be used for mild to moderate chronic pain. However, unlike prescription drugs, they are not addictive and do not dull the senses. In addition, they can help heal the nervous system as well as relieving pain. The following herbal remedies have been known to provide pain relief:

Capsaisin: is found naturally in cayenne pepper. (Its cream or gel form may be able to relieve some arthritic pain.)

Bromelain : reduce inflammation.

Curcumin: reduces inflammation.

Kava kava: helps relax the body.

Pine-bark and grape-seed extracts: reduces inflammation.

Pain-relief tea: is composed of white willow bark, chamomile, skullcap, valerian root and licorice root. (This herbal preparation may be effective in relieving normal aches and pain. However, persons with high blood pressure or those allergic to aspirin should avoid using this preparation.)

Nutritional therapy

Diet and nutrition can play important roles in controlling chronic pain. Patients with chronic pain sometimes find relief just by eating healthy foods and by adding nutritional supplements with pain-killing properties. A diet high in fiber and complex carbohydrates is recommended. Because inflammation is often caused by allergic reactions, patients should eliminate allergic foods from their diets . They should also avoid foods high in fats or margarine, red meat, dairy products, shellfish, alcohol, and coffee. In addition, they may consider taking one of the following nutritional supplements: flaxseed oil, bromelain, calcium taken with magnesium, vitamin C taken with bioflavonoids , and glucosamine . Glucosamine sulfate is one of the best natural remedies available for arthritic pain. Studies have shown that it effectively reduces pain and improves joint movement in 80% of arthritic patients. It works by healing and regenerating new connective tissues damaged by the inflammatory process. It may also increase the level of endorphins, the body's natural painkillers, and reduces inflammation in most arthritic patients. Recently, researchers also confirmed what thousands of people with arthritis have known for a long time — that cod liver oil eases the pain of arthritis. A new study says that the omega-3 fatty acids in cod liver oil break down joint cartilage, slowing destruction of the joints and easing pain. This has been good news for arthritis sufferers who can not tolerate the prescription drugs available for arthritis treatment.

Homeopathy

Depending on a patient's specific condition, a homeopathic physician may prescribe one of the following medications for pain management:

Arnica: for treatment of acute pain after an injury.

Hypericum: for treatment of pain in nerves, fingers or toes after injury or surgery.

Ledum: for treatment of pain associated with black- and-blue bruises and puncture wounds.

Acupuncture

Acupuncture involves inserting needles at various points on the skin of the body. These needles direct chi (life force) to organs or functions of the body. This therapy possibly works by triggering the release of endorphins, therefore dulling the perception of pain. Acupuncture can effectively reduce most chronic pain. However, it may require up to 10 sessions before results are noticeable. A 2002 study showed that acupuncture worked well for chronic neck pain and range of motion, but that its long-term effects were limited. It is important that patients request disposable needles to prevent transmission of AIDS, hepatitis , and other infectious diseases.

Acupressure

There are some acupressure techniques that patients can train themselves to do to help relieve pain. Using thumbs or fingers to apply pressure at appropriate acupressure points in the body, a person can release muscular tension in the head, neck or shoulder; calm the nervous system and relieve painful symptoms. Like acupuncture, acupressure probably works by releasing endorphins.

Massage

Massage involves using physical manipulation techniques to make various parts of the body, such as muscles, connective tissues, and vertebrae, work together and function properly. This form of therapy may effectively reduce stress and physical pain.

Chiropractic

Chiropractors treat patients by manipulating joints and the spine. It is believed that pain, especially back pain, is caused by misalignment of the spine. This form of treatment is most effective in patients with persistent back pain and neck problems. It is also effective in patients with acute, uncomplicated low back pain .

Relaxation therapy

Relaxation techniques include meditation, yoga, guided imagery, biofeedback , and hypnotherapy . When practiced regularly, these techniques have been shown to relax muscles and reduce tension and stress-related pain.

Lifestyle changes

Lifestyles can be changed to include a healthier diet and regular exercise . Regular exercise, aside from relieving stress, has been shown to increase endorphins.

Hydrotherapy

This form of therapy uses hot and cold compresses, whirlpools, saunas, and alternating cold/warm showers or body wraps to reduce the soreness of aching joints, inflamed muscles, chronic muscle strains, and backache. Some of these treatments can be done at home.

Allopathic treatment

There are many drugs aimed at preventing or treating pain. Nonopioid analgesics, narcotic analgesics, corticosteroids, anticonvulsant drugs, and tricyclic antidepressants work by blocking the production, release, or uptake of neurotransmitters. Nonopioid analgesics are used for treatment of minor pain. They include common over-the-counter medications such as aspirin, acetaminophen (Tylenol), and ibuprofen (Advil). Narcotic analgesics such as codeine, morphine, and methadone are used for more severe pain, such as cancer pain. These medications are available with a doctor's prescription. Initially developed to treat seizures and depression, some anticonvulsants and antidepressants now also have pain-killing applications. Finally, corticosteroid injections directly into or near the nerve that is transmitting the pain signal are reserved for intractable (unrelenting) pain that is not treatable by other medications.

Drugs are not always effective in controlling pain. Surgical methods are used as a last resort if drugs and local anesthetics fail. Electrode implants are the least destructive surgical procedure. However, this method may not completely control pain and is not used frequently. Other surgical techniques involve destroying or severing the nerve, but the use of this technique is limited by side effects, including unpleasant numbness.

Expected results

Successful pain treatment is highly dependent on successful resolution of the pain's cause. Acute pain will stop when an injury heals or when an underlying problem is treated successfully. Chronic pain and abnormal pain are more difficult to treat, and it may take longer to find a successful resolution. Some pain is intractable and will require extreme measures for relief. In 2002, several health care organizations got together to form a panel charged with working on standards for evaluating effectiveness of pain management for patients who suffer from cancer, arthritis, and back pain. The standards will help physicians and others better measure patients' pain and effectiveness of pain management drugs and techniques.

Prevention

Pain is generally preventable only to the degree that the cause of the pain is preventable; diseases and injuries are often unavoidable. However, increased pain, pain from surgery and other medical procedures, and continuing pain are preventable through drug treatments and alternative therapies.

For many years, experts thought that arthritis patients should not exercise because it would damage their joints. However, a 2002 report said that regular low-impact exercise such as water aerobics or riding a stationary bicycle can actually help arthritic patients prevent pain.

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pain

pain The International Association for The Study of Pain has provided the following definition of pain, which is used world-wide amongst scientists and clinicians interested in pain.

Pain is ‘an unpleasant sensory and emotional experience associated with actual or potential damage, or described in terms of such damage. Pain is always subjective. Each individual learns the application of the word through experiences relating to injury in early life’.

Noxious stimulation of a part of the body gives rise to electrical activity in the nervous system, extending from the periphery to the brain. Receptors and pathways dedicated to the nerve impulses giving rise to pain are described as components of somatic sensation and of visceral sensation. That activity is modulated within the central nervous system, both within the dorsal horns of the grey matter of the spinal cord and at higher levels. In this manner the input to the brain generated by noxious stimulation peripherally may be enhanced, diminished, or even, under certain circumstances, abolished — for example, in the heat of battle or a game of football. Thus, although noxious stimulation occurs, pain may not be felt at the time; such a mechanism clearly has value for survival of the individual in certain cases.

Our understanding of the physiology of pain control owes a great deal to the work of Melzack and Wall of some thirty-five years ago. Respectively a psychologist/physiologist and neurophysiologist, they proposed the gate-control theory of pain, which brought together previous work on the role of the nervous system in the generation of pain. They stated that within the dorsal horn of the spinal cord there are transmission cells (‘Trans cell’ in the figure) and that, as a result of tissue damage and stimulation, nerve impulses pass to those cells, which project further nerve impulses to the brain, where pain is experienced. The level of activity of the transmission cells is controlled by small adjacent cells which either excite or inhibit them. In turn the level of activity of the smaller cells is determined by the extent to which they are stimulated by nerve impulses from the body or the brain. Large diameter nerve fibres (beta fibres), which are stimulated by touch, excite the small inhibitory cells (white circles in the figure) adjacent to the transmission cells. In contrast, tissue injury excites other (A delta and C) nerve fibres. The former are large diameter fibres which conduct rapidly and the latter are small diameter fibres which conduct slowly. Both stimulate the transmission cell and small excitatory cells (black circles in the figure). Therefore in an acute injury, for example when the thumb is struck by a hammer, the A delta and C fibre activity exceeds the activity in beta fibres and pain is felt. When the injured part is rubbed vigorously the pain lessens and it does so because rubbing the skin stimulates beta fibres to the point where their level of stimulation of the small inhibitory cells exceeds that of the stimulation by the A delta and C fibres of the small excitatory cells. As a result, the activity of the transmission cell is reduced or ceases. This mechanism is involved when clinicians use transcutaneous electrical nerve stimulation (TENS) to relieve pain. Neurons descending from the brain may also excite or inhibit activity of the transmission cells within the spinal cord by influencing the small adjacent excitatory and inhibitory cells. For example, in states of emotional calmness, inhibition of transmission cell activity occurs, and less pain is experienced than in states of anxiety, when the activity of the transmission cells is increased by stimulation of the small excitatory cells.

In some situations pain may be felt when part of the body is missing, for example after the amputation of a limb or breast. Such ‘phantom pains’ are located in the absent part at a site where pain may have been felt before the part was lost. How then can pain, which is at times chronic and excruciating, be experienced in a limb that does not exist as a physical reality? The answer lies in the way the brain functions. Activity in areas of the brain concerned with sensory activity in the missing limb continues despite the absence of the limb, and gives rise to a phantom. If in addition central pain processes are active, phantom pain is experienced in the phantom limb. Such pain may be eliminated by stimulation of the sensory cerebral cortex but not by the division of nerves or the spinal cord. This supports the view that, although most people believe that pain actually exists at a site in the body that hurts, it is in fact a part of consciousness and the result of brain activity.

Until recently it was thought that the sensory and emotional elements of pain experience were linked solely to specific areas of the brain, namely the sensory and the emotional cortex, respectively. However, recent work using non-invasive brain imaging techniques — for example positron emission scanning — has revealed this model to be too simple. It is true that within the brain there is a degree of functional specialization for pain, but this is only part of the story. For example, damage to one half of the cerebral cortex does not necessarily abolish pain sensations from the opposite side of the body, and damage to areas of the brain associated with emotion does not necessarily remove the emotional component of pain. The reason for these apparent anomalies seems to lie in the fact that pain is generated within a widely distributed system or neuronal network. In this way, the brain detects tissue injury even when there is considerable damage to the nervous system. The brain functions as an active system, which filters, selects, and integrates sensory input against the background of lifelong experiences, both physical and emotional, which are preserved in the systems devoted to memory. One brain output from this process is pain.

Pain therefore occurs only in the conscious individual, and it is essential for survival. A small but unfortunate number of people are born without the capacity to feel pain. As a result they suffer horrific injuries in childhood and die young as a result of accidents or undiagnosed disorders, which in normal people give rise to pain.

In everyday life pain is recognized in two forms, namely acute pain and chronic pain. The former has a protective function. It alerts us to damage to the body, it increases our level of arousal, it directs our attention to the cause of the pain, and generates behaviour that leads to an escape from it. The chief emotion associated with acute pain is anxiety, and this subsides when pain is relieved and the cause is understood. In contrast, chronic pain does not appear to the sufferer to have any purpose and indeed has negative qualities. It gives rise to feelings of anxiety and at times of depression. The behaviours generated include withdrawal from social activities and a search for relief. The latter may well lead the sufferer to move from one doctor to another and to non-medical practitioners in the hope of pain relief. At times that process itself may generate more physical suffering through unnecessary investigation and the end result is pain, despair, and depression.

Both acute and chronic forms of pain are familiar, but in addition pain occurs in two other, quite different situations. It may occur as a symptom in a depressive illness. In other words it is not, as is commonly thought in such situations, that depression has developed because pain is being experienced but, in fact, the pain is part of a primary depressive illness. Up to half of those who develop depressive illnesses experience physical symptoms unrelated to any obvious underlying pathology, and of those symptoms pain is the most common. The failure of doctors to appreciate this fact does occasionally lead to a prolonged search for a physical cause for pain because its presence overshadows other features of a depressive illness.

Pain occurs in individual's experiencing anxiety, or emotional tension. For example, tension headaches are very common. The presence of anxiety in a pain sufferer tends both to increase the severity of pain experienced and to reduce the individual's tolerance or ability to cope with it.

Pain may occur in the absence of an obvious physical cause and where the features of a mental illness are not detectable. Individuals with this type of pain may have had a trivial injury but the level of pain and disability with which they present is out of all proportion to the severity of that injury. In addition, the behaviour shown by the sufferer reveals considerable dependence upon others, loss of willingness to take responsibility for themselves, their home, and their work, and a preoccupation with a search for a ‘cure’ for the pain, which they regard firmly as physical in origin.

Consideration of pain problems in which an underlying physical cause is either minimal or absent highlights the fact that when trying to understand pain it is necessary not only to consider its sensory aspects, but also its emotional ones. Indeed it has been said that to ignore the emotional aspects of pain is to look at only one part of the problem, and probably not the most important part at that. The definition of pain given earlier reinforces this point.

As a consequence of the need to encompass the physical, psychological, and social aspects of pain experience, clinicians and pain researchers have developed what is known as the biopsychosocial model of pain. It is based upon what we know about the generation and control of pain within the nervous system, and also its psychological aspects and the social factors that influence the thinking of individuals about pain and their behaviour. This approach to pain has lead to the development of powerful psychological tools for pain management, which come under the broad heading of cognitive–behavioural theory and practice.

Consideration of socio-cultural and learning factors reveals that learning about pain takes place within a definite social context, and the way each of us behaves when in pain reflects that fact. At a national level it is customary in general for those who are from Northern European countries to regard complaints about pain, especially amongst men, as a weakness of character. In contrast, in Southern European countries to complain about pain is regarded as beneficial to the sufferer. These are very broad generalizations but do have some basis in fact. An important psychological mechanism by which we learn the behaviours we exhibit when in pain is defined as operant learning. It is a process by which overt behavioural responses to a stimulus are significantly influenced by their consequences, including the responses of others to them.

Operant learning is well illustrated by the effects of a simple injection upon a child. The sight of the needle and the pain experienced is an ‘unconditioned stimulus’ and as a response to it the child cries. On the next occasion the child cries at the sight of the syringe and needle, which have become ‘the conditioned stimulus’. If crying leads to the abandonment of the injection the child has developed a ‘conditioned escape response’. Seeing another child crying before an injection which is then not given leads to another type of learning — ‘an observational learning model’.

In some individuals such mechanisms lead to the development of pain behaviours that have a negative effect upon their lives — for example, the excessive use of rest to relieve pain, or the abuse of powerful narcotic-related drugs may actually lead to increasing chronicity of pain and disability. To counter such developments psychologists have developed techniques based upon operant conditioning, which are designed to reverse maladaptive pain behaviours and to replace them by adaptive behaviours. In other words, their techniques involve the use of learning of behaviour designed to lead to coping with pain and everyday life rather than withdrawing from them. Put in simple terms, ‘good behaviour is rewarded and bad behaviour is punished’.

Operant conditioning has been criticized on the grounds that it does not take sufficient account of mental activity. In other words, individuals have thoughts about pain and attitudes towards it. They draw on memories of past experience when in pain, and this leads to thinking and behaviour, which is the result of those experiences. Such thoughts and attitudes, or cognitions, as they are called, cannot be ignored when a clinician is evaluating a person in pain and planning their treatment. For this reason, a purely behavioural approach has been replaced by a cognitive–behavioural approach to pain analysis and management. The main cognitive elements that have been identified include beliefs about pain and its causes, beliefs about the extent to which the individual feels he or she has control over pain, and the extent to which individuals believe that they are able to function despite pain. Therefore, self-efficiency is a significant factor in determining ability to cope.

People in pain often develop what are described by psychologists as ‘cognitive errors’. For example, they may indulge in what is known as ‘catastrophizing’. In other words they develop an unnecessarily negative view of their condition and its likely outcome. In such a state they tend to focus to a extent upon the negative features of their disorder. It has been demonstrated that negative qualities of thought, and catastrophizing in particular, are consistently linked to the development of depression in chronic pain disorders. The manipulation of coping mechanisms is of great significance when considering the management of pain and especially of chronic pain. We are all familiar with coping strategies, some of which are regarded as active — for example, indulging in active and distracting behaviour, whereas others are passive — for example, taking rest or medicines. If the strategy used maximizes function in the presence of pain and reduces anxiety, then it is said to be adaptive. On the other hand, if the strategies used involve too much rest, too great a dependence on medication or on others, or conversely too much activity which provokes excessive pain, they are maladaptive. Cognitive therapies involve changing thoughts and attitudes about pain with a view to changing self-management in the direction of adaptive behaviour: a change which often leads to a lessening of pain.

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Pain

Pain

Definition

Pain is an unpleasant feeling that is conveyed to the brain by nerves in the body.

Description

Pain arises from any number of situations. Injury is a major cause, but pain may also arise from an illness. It may accompany a psychological condition, such as depression, or may even occur in the absence of a recognizable trigger. The discomfort signals actual or potential injury to the body. However, pain is more than a sensation or the physical awareness of pain; it also includes perception, the subjective interpretation of the discomfort. Perception gives information on the pain's location, intensity, and something about its nature. The various conscious and unconscious responses to both sensation and perception, including the emotional response, add further definition to the overall concept of pain.

Acute pain

Acute pain often results from tissue damage, such as a skin burn or broken bone. Acute pain can also be associated with headaches or muscle cramps . This type of pain usually goes away as the injury heals or the cause of the pain (stimulus) is removed. To understand acute pain, it is necessary to understand the nerves that support it. Nerve cells, or neurons, perform many functions in the body. Although their general purpose, providing an interface between the brain and the body, remains constant, their capabilities vary widely. Certain types of neurons are capable of transmitting a pain signal to the brain. As a group, these pain-sensing neurons are called nociceptors, and virtually every surface and organ of the body is wired with them. The central part of these cells is located in the spine, and they send threadlike projections to every part of the body. Nociceptors are classified according to the stimulus that prompts them to transmit a pain signal. Thermoreceptive nociceptors are stimulated by temperatures that are potentially tissue damaging. Mechanoreceptive nociceptors respond to a pressure stimulus that may cause injury. Polymodal nociceptors are the most sensitive and can respond to temperature and pressure. Polymodal nociceptors also respond to chemicals released by the cells in the area from which the pain originates.

Nerve cell endings, or receptors, are responsible for pain sensation. A stimulus at this part of the nociceptor unleashes a cascade of neurotransmitters (chemicals that transmit information within the nervous system) in the spine. Each neurotransmitter has a purpose. For example, substance P relays the pain message to nerves leading to the spinal cord and brain. These neurotransmitters may also stimulate nerves leading back to the site of the injury. This response prompts cells in the injured area to release chemicals that not only trigger an immune response but also influence the intensity and duration of the pain.

Chronic and abnormal pain

Chronic pain refers to pain that persists after an injury heals, cancer pain, pain related to a persistent or degenerative disease, and long-term pain from an unidentifiable cause. It is estimated that one in three people
in the United States experiences chronic pain at some point in their lives. Of these people, approximately 50 million are either partially or completely disabled. Chronic pain may be caused by the body's response to acute pain. In the presence of continued stimulation of nociceptors, changes occur within the nervous system. Changes at the molecular level are dramatic and may include alterations in genetic transcription of neurotransmitters and receptors. These changes may also occur in the absence of an identifiable cause; one of the frustrating aspects of chronic pain is that the stimulus may be unknown. For example, the stimulus cannot be medically identified in as many as 85 percent of individuals suffering from lower back pain.

Other types of abnormal pain include allodynia, hyperalgesia, and phantom limb pain. These types of pain often arise from some damage to the nervous system (neuropathic). Allodynia refers to a feeling of pain in response to a normally harmless stimulus. For example, some individuals who have suffered nerve damage as a result of viral infection experience unbearable pain from just the light weight of their clothing. Hyperalgesia is somewhat related to allodynia in that the response to a painful stimulus is extreme. In this case, a mild pain stimulus, such as a pinprick, causes a maximum pain response. Phantom limb pain occurs after a limb is amputated; although an individual may be missing the limb, the nervous system continues to perceive pain originating from the area.

Demographics

Pain is experienced by all age groups, both sexes, and all races and ethnic groups.

Causes and symptoms

Pain is the most common symptom of injury and disease, and descriptions can range in intensity from a mere ache to unbearable agony. Nociceptors have the ability to convey information to the brain that indicates the location, nature, and intensity of the pain. For example, stepping on a nail sends an information-packed message to the brain: the foot has experienced a puncture wound that hurts a lot. Pain perception also varies depending on the location of the pain. The kinds of stimuli that cause a pain response on the skin include pricking, cutting, crushing, burning, and freezing. These same stimuli would not generate much of a response in the intestine. Intestinal pain arises from stimuli such as swelling, inflammation, and distension.

When to call the doctor

Parents should notify their physician or pediatrician if any of the following occurs:

The child is in severe pain.

The child has pain that lasts for more than three days.

Parents have questions or concerns about their child's treatment or condition.

The child is in the hospital and the parent thinks he or she is in pain. The sooner the pain is treated, the easier it is to control.

Diagnosis

Pain is considered in view of other symptoms and individual experiences. An observable injury, such as a broken bone, may be a clear indicator of the type of pain a person is suffering. Determining the specific cause of internal pain is more difficult. Other symptoms, such as fever or nausea , help narrow the possibilities. In some cases, such as lower back pain, a specific physiological cause may not be identified. Diagnosis of the disease causing a specific pain is further complicated by the fact that pain can be referred to (felt at) a skin site that does not seem to be connected to the site of the pain's origin. For example, pain arising from fluid accumulating at the base of the lung may be referred to the shoulder.

Since pain is a subjective experience, it may be very difficult to communicate its exact quality and intensity to other people. There are no diagnostic tests that can determine the quality or intensity of an individual's pain. Therefore, a medical examination includes a lot of questions about where the pain is located, its intensity, and its nature. Questions are also directed at what kinds of things increase or relieve the pain, how long it has lasted, and whether there are any variations in it. An individual may be asked to use a pain scale to describe the pain. One such scale assigns a number to the pain intensity; for example, 0 may indicate no pain, and 10 may indicate the worst pain the person has ever experienced. Scales are modified for infants and children to accommodate their level of comprehension.

A subsequent method of evaluating pain in children up to age four years was as of 2004 set to be implemented in 60 hospitals in the Netherlands. The Pain Observation Scale for Young Children, called POCIS, measures pain levels according to children's behavior in seven categories: facial expressions, crying, breathing, torso movements, movements in the arms and fingers and in the legs and toes, and restlessness. Physicians and nurses observe the intensity of these behaviors and calculate a pain severity score ranging from 0 to 7. Researchers
from the University of Amsterdam who developed the scale said that existing behavioral pain measures were created for premature neonates or infants and may not be appropriate for older children. Some of those measures are upsetting for children because they require restraint or physical contact by a healthcare professional.

Alternative treatment

Both physical and psychological aspects of pain can be dealt with through alternative treatment. Some of the most popular treatment options include acupressure and acupuncture, massage, chiropractic, and relaxation techniques, such as yoga , hypnosis, and meditation. Herbal therapies are increasingly recognized as viable options; for example, capsaicin, the component that makes cayenne peppers spicy, is used in ointments to relieve the joint pain associated with arthritis. Contrast hydrotherapy can also be very beneficial for pain relief. Lifestyles can be changed to incorporate a healthier diet and regular exercise . Regular exercise, aside from relieving stress, has been shown to increase endorphins, painkillers naturally produced in the body.

Prognosis

Successful pain treatment is highly dependent on successful resolution of the pain's cause. Acute pain will stop when an injury heals or when an underlying problem is treated successfully. Chronic pain and abnormal pain are more difficult to treat, and it may take longer to find a successful resolution. Some pain is intractable and requires extreme measures for relief.

Prevention

Pain is generally preventable only to the degree that the cause of the pain is preventable; diseases and injuries are often unavoidable. However, increased pain, pain from surgery and other medical procedures, and continuing pain are preventable through drug treatments and alternative therapies.

Parental concerns

If a child has a lot of pain, it is likely that more can be done to help. The first step is for parents to tell the child's doctor or nurse what their concerns are. They can ask what more can be done for the child to control pain. If parents are still concerned about their child's pain control, they can request a meeting with the doctor. Parents should list their concerns as clearly as possible. They should take a constructive approach and seek to form a partnership with the healthcare team in managing the child's pain. For parents who are still not satisfied with what is being done, some type of formal complaint to the hospital may be unavoidable. Pain management is the right of every child. Parents working with health providers are the best advocates for this right. The U.S. Department of Health and Human Services Agency for Health Care Policy and Research has developed guidelines for pain management. These guidelines establish a standard of care that should be followed. Parents can get a copy from the hospital library or directly from the government.

KEY TERMS

Acute pain—Pain in response to injury or another stimulus that resolves when the injury heals or the stimulus is removed.

Chronic pain—Pain that lasts over a prolonged period and threatens to disrupt daily life.

Neuron—The fundamental nerve cell of the nervous system.

Neurotransmitters—Chemicals in the brain that transmit nerve impulses.

Nociceptor—A nerve cell that is capable of sensing pain and transmitting a pain signal.

Referred pain—Pain that is experienced in one part of the body but originates in another organ or area. The pain is referred because the nerves that supply the damaged organ enter the spine in the same segment as the nerves that supply the area where the pain is felt.

Stimulus—Anything capable of eliciting a response in an organism or a part of that organism.

PERIODICALS

O'Rourke, Deborah. "The Measurement of Pain in Infants, Children, and Adolescents: From Policy to Practice." Physical Therapy (June 2004): 560–70.

Springen, Karen. "Small Patients, Big Pain: Ten Million American Children Suffer Chronic or Recurrent Pain. Treating Them Poses Special Challenges. Now Doctors and Researchers are Learning How to Help." Newsweek (May 19, 2003): 54.

Williams, Mathew E. "Trouble Underfoot: Heel Pain in Children: Practitioners Must Have a High Index of Suspicion and Conduct a Thorough Workup to Determine the True Cause of a Child's Symptoms." Biomechanics (July 1, 2004): 26.

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Pain

Gale Encyclopedia of Medicine, 3rd ed.
COPYRIGHT 2006 Thomson Gale

Pain

Definition

Pain is an unpleasant feeling that is conveyed to the brain by sensory neurons. The discomfort signals actual or potential injury to the body. However, pain is more than a sensation, or the physical awareness of pain; it also includes perception, the subjective interpretation of the discomfort. Perception gives information on the pain's location, intensity, and something about its nature. The various conscious and unconscious responses to both sensation and perception, including the emotional response, add further definition to the overall concept of pain.

Description

Pain arises from any number of situations. Injury is a major cause, but pain may also arise from an illness. It may accompany a psychological condition, such as depression, or may even occur in the absence of a recognizable trigger.

Acute pain

Acute pain often results from tissue damage, such as a skin burn or broken bone. Acute pain can also be associated with headaches or muscle cramps. This type of pain usually goes away as the injury heals or the cause of the pain (stimulus) is removed.

To understand acute pain, it is necessary to understand the nerves that support it. Nerve cells, or neurons, perform many functions in the body. Although their general purpose, providing an interface between the brain and the body, remains constant, their capabilities vary widely. Certain types of neurons are capable of transmitting a pain signal to the brain.

As a group, these pain-sensing neurons are called nociceptors, and virtually every surface and organ of the body is wired with them. The central part of these cells is located in the spine, and they send threadlike projections to every part of the body. Nociceptors are classified according to the stimulus that prompts them to transmit a pain signal. Thermoreceptive nociceptors are stimulated by temperatures that are potentially tissue damaging. Mechanoreceptive nociceptors respond to a pressure stimulus that may cause injury. Polymodal nociceptors are the most sensitive and can respond to temperature and pressure. Polymodal nociceptors also respond to chemicals released by the cells in the area from which the pain originates.

Nerve cell endings, or receptors, are at the front end of pain sensation. A stimulus at this part of the nociceptor unleashes a cascade of neurotransmitters (chemicals that transmit information within the nervous system) in the spine. Each neurotransmitter has a purpose. For example, substance P relays the pain message to nerves leading to the spinal cord and brain. These neurotransmitters may also stimulate nerves leading back to the site of the injury. This response prompts cells in the injured area to release chemicals that not only trigger an immune response, but also influence the intensity and duration of the pain.

Chronic and abnormal pain

Chronic pain refers to pain that persists after an injury heals, cancer pain, pain related to a persistent or degenerative disease, and long-term pain from an unidentifiable cause. It is estimated that one in three people in the United States will experience chronic pain at some point in their lives. Of these people, approximately 50 million are either partially or completely disabled.

Chronic pain may be caused by the body's response to acute pain. In the presence of continued stimulation of nociceptors, changes occur within the nervous system. Changes at the molecular level are dramatic and may include alterations in genetic transcription of neurotransmitters and receptors. These changes may also occur in the absence of an identifiable cause; one of the frustrating aspects of chronic pain is that the stimulus may be unknown. For example, the stimulus cannot be identified in as many as 85% of individuals suffering lower back pain.

Scientists have long recognized a relationship between depression and chronic pain. In 2004, a survey of California adults diagnosed with major depressive disorder revealed that more than one-half of them also suffered from chronic pain.

Other types of abnormal pain include allodynia, hyperalgesia, and phantom limb pain. These types of pain often arise from some damage to the nervous system (neuropathic). Allodynia refers to a feeling of pain in response to a normally harmless stimulus. For example, some individuals who have suffered nerve damage as a result of viral infection experience unbearable pain from just the light weight of their clothing. Hyperalgesia is somewhat related to allodynia in that the response to a painful stimulus is extreme. In this case, a mild pain stimulus, such as a pin prick, causes a maximum pain response. Phantom limb pain occurs after a limb is amputated; although an individual may be missing the limb, the nervous system continues to perceive pain originating from the area.

Causes and symptoms

Pain is the most common symptom of injury and disease, and descriptions can range in intensity from a mere ache to unbearable agony. Nociceptors have the ability to convey information to the brain that indicates the location, nature, and intensity of the pain. For example, stepping on a nail sends an information-packed message to the brain: the foot has experienced a puncture wound that hurts a lot.

Pain perception also varies depending on the location of the pain. The kinds of stimuli that cause a pain response on the skin include pricking, cutting, crushing, burning, and freezing. These same stimuli would not generate much of a response in the intestine. Intestinal pain arises from stimuli such as swelling, inflammation, and distension.

Diagnosis

Pain is considered in view of other symptoms and individual experiences. An observable injury, such as a broken bone, may be a clear indicator of the type of pain a person is suffering. Determining the specific cause of internal pain is more difficult. Other symptoms, such as fever or nausea, help narrow down the possibilities. In some cases, such as lower back pain, a specific cause may not be identifiable. Diagnosis of the disease causing a specific pain is further complicated by the fact that pain can be referred to (felt at) a skin site that does not seem to be connected to the site of the pain's origin. For example, pain arising from fluid accumulating at the base of the lung may be referred to the shoulder.

Since pain is a subjective experience, it may be very difficult to communicate its exact quality and intensity to other people. There are no diagnostic tests that can determine the quality or intensity of an individual's pain. Therefore, a medical examination will include a lot of questions about where the pain is located, its intensity, and its nature. Questions are also directed at what kinds of things increase or relieve the pain, how long it has lasted, and whether there are any variations in it. An individual may be asked to use a pain scale to describe the pain. One such scale assigns a number to the pain intensity; for example, 0 may indicate no pain, and 10 may indicate the worst pain the person has ever experienced. Scales are modified for infants and children to accommodate their level of comprehension.

Treatment

There are many drugs aimed at preventing or treating pain. Nonopioid analgesics, narcotic analgesics, anticonvulsant drugs, and tricyclic antidepressants work by blocking the production, release, or uptake of neurotransmitters. Drugs from different classes may be combined to handle certain types of pain.

Nonopioid analgesics include common over-the-counter medications such as aspirin, acetaminophen (Tylenol), and ibuprofen (Advil). These are most often used for minor pain, but there are some prescription-strength medications in this class.

Narcotic analgesics are only available with a doctor's prescription and are used for more severe pain, such as cancer pain. These drugs include codeine, morphine, and methadone. Addiction to these painkillers is not as common as once thought. Many people who genuinely need these drugs for pain control typically do not become addicted. However, narcotic use should be limited to patients thought to have a short life span (such as people with terminal cancer) or patients whose pain is only expected to last for a short time (such as people recovering from surgery). In August 2004, the Drug Enforcement Administration (DEA) issued new guidelines to help physicians prescribe narcotics appropriately without fear of being arrested for prescribing the drugs beyond the scope of their medical practice. DEA is trying to work with physicians to ensure that those who need to drugs receive them but to ensure opioids are not abused.

Anticonvulsants, as well as antidepressant drugs, were initially developed to treat seizures and depression, respectively. However, it was discovered that these drugs also have pain-killing applications. Furthermore, since in cases of chronic or extreme pain, it is not unusual for an individual to suffer some degree of depression; antidepressants may serve a dual role. Commonly prescribed anticonvulsants for pain include phenytoin, carbamazepine, and clonazepam. Tricyclic antidepressants include doxepin, amitriptyline, and imipramine.

Intractable (unrelenting) pain may be treated by injections directly into or near the nerve that is transmitting the pain signal. These root blocks may also be useful in determining the site of pain generation. As the underlying mechanisms of abnormal pain are uncovered, other pain medications are being developed.

Drugs are not always effective in controlling pain. Surgical methods are used as a last resort if drugs and local anesthetics fail. The least destructive surgical procedure involves implanting a device that emits electrical signals. These signals disrupt the nerve and prevent it from transmitting the pain message. However, this method may not completely control pain and is not used frequently. Other surgical techniques involve destroying or severing the nerve, but the use of this technique is limited by side effects, including unpleasant numbness.

Alternative treatment

Both physical and psychological aspects of pain can be dealt with through alternative treatment. Some of the most popular treatment options include acupressure and acupuncture, massage, chiropractic, and relaxation techniques such as yoga, hypnosis, and meditation. Herbal therapies are gaining increased recognition as viable options; for example, capsaicin, the component that makes cayenne peppers spicy, is used in ointments to relieve the joint pain associated with arthritis. Contrast hydrotherapy can also be very beneficial for pain relief.

Lifestyles can be changed to incorporate a healthier diet and regular exercise. Regular exercise, aside from relieving stress, has been shown to increase endorphins, painkillers naturally produced in the body.

Prognosis

Successful pain treatment is highly dependent on successful resolution of the pain's cause. Acute pain will stop when an injury heals or when an underlying problem is treated successfully. Chronic pain and abnormal pain are more difficult to treat, and it may take longer to find a successful resolution. Some pain is intractable and will require extreme measures for relief.

Prevention

Pain is generally preventable only to the degree that the cause of the pain is preventable. For example, improved surgical procedures, such as those done through a thin tube called a laparascope, minimize post-operative pain. Anesthesia techniques for surgeries also continuously improve. Some disease and injuries are often unavoidable. However, pain from some surgeries and other medical procedures and continuing pain are preventable through drug treatments and alternative therapies.

KEY TERMS

Acute pain— Pain in response to injury or another stimulus that resolves when the injury heals or the stimulus is removed.

Chronic pain— Pain that lasts beyond the term of an injury or painful stimulus. Can also refer to cancer pain, pain from a chronic or degenerative disease, and pain from an unidentified cause.

Neuron— A nerve cell.

Neurotransmitters— Chemicals within the nervous system that transmit information from or between nerve cells.

Nociceptor— A neuron that is capable of sensing pain.

Referred pain— Pain felt at a site different from the location of the injured or diseased part of the body. Referred pain is due to the fact that nerve signals from several areas of the body may "feed" the same nerve pathway leading to the spinal cord and brain.

Stimulus— A factor capable of eliciting a response in a nerve.

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Pain

Gale Encyclopedia of Psychology
COPYRIGHT 2001 The Gale Group Inc.

Pain

Physical suffering resulting from some sort of injury or disease, experienced through the central nervous system.

Pain is a complex phenomenon that scientists are still struggling to understand. Its purpose is to alert the body of damage or danger to its system, yet scientists do not fully understand the level and intensity of pain sometimes experienced by people. Long-lasting, severe pain does not serve the same purpose as acute pain, which triggers an immediate physical response. Pain that persists without diminishing over long periods of time is known as chronic pain. It is estimated that almost one-third of all Americans suffer from some form of chronic pain. Of these, 70 million have back pain, 36 million have arthritis, 20 million suffer from migraine headaches, and at least 800,000 Americans suffer severe pain associated with the growth of cancerous tumors. An additional kind of pain is psychological pain. Recent research has shown that the chemicals produced by anxiety are similar to those that are released in response to physical injury.

Pain signals travel through the body along billions of special nerve cells reserved specifically for transmitting pain messages. These cells are known as nociceptors. The chemical neurotransmitters carrying the message include prostaglandins, bradykinin—the most painful substance known to humans—and a chemical known as P, which stands for pain. Prostaglandins are manufactured from fatty acids in nearly every tissue in the body. Analgesic pain relievers, such as aspirin and ibuprofen, work by inhibiting prostaglandin production.

After an injury, cells near the trauma site release these chemicals into the central nervous system . In the spinal cord, they are carried by the dorsal horn, and it is at this point that the body pulls away from the source of the pain. When the signal reaches the brain , it is first processed by the thalamus and then passed to the cerebral cortex. Here, the brain fully processes the information, locates its source in the body, and begins sending signals to relieve the pain.

As they travel, the pain messages are sorted according to severity. Recent research has discovered that the body has two distinct pathways for transmitting pain messages. The epicritic system is used to transmit messages of sudden, intense pain, such as that caused by cuts or burns. The neurons that transmit such messages are called A fibers, and they are built to transmit messages quickly. The protopathic system is used to transmit less severe messages of pain, such as the kind one might experience from over-strenuous exercise. The C fibers of the protopathic system do not send messages as quickly as A fibers.

In 1965, Ronald Melzack and Patrick Wall, leading pain researchers at the Massachusetts Institute of Technology, proposed what has come to be known as the gate theory of pain. This theory holds that the nervous system has the capacity to process only limited amounts of information at a time. For example, if the body is over-whelmed by multiple messages, the nervous system will "shut down" certain messages. This would explain why rubbing an injury often lessens its pain. The rubbing, in essence, competes with the injury for space in the nervous system.

One application of the gate theory is the use of small bursts of electricity to help manage pain. Experiments were first conducted on animals, whose brains were stimulated electronically at certain points, shutting down their capacity to feel pain. The animals were then operated on using no anesthetic. This method has been adapted for humans as well and has led to the development of a pain relief method known as transcutaneous electrical nerve stimulation, or TENS. In this technique, pain sufferers are jolted with tiny bits of electricity at strategic points. As predicted by the gate theory, the nerve endings at the point of the shock are overwhelmed and divert some of the space in the central nervous system to processing it, thereby relieving the original pain.

Chronic pain, on the other hand, presents its own set of problems. Treating chronic pain is difficult because by its very nature, such pain damages the central nervous system, making it weaker and more susceptible to pain. This residue of pain is called pain memory . Problems also arise when nerve cells are damaged by chemotherapy, diabetes, shingles, and other diseases. And in the case of arthritis and other inflammatory diseases, the body's threshold for pain is lowered, thus causing increased pain from "less" stimuli.

Treatments for pain vary widely. For mild pain, the most common form of treatment is aspirin, a medication discovered in the 19th century and derived from salicin, a chemical found in the bark of the willow tree. Today, there are several aspirin-like drugs on the market for the relief of minor, inflammatory pain, including ibuprofen and acetaminophen. For more severe pain, opiates—derived from the opium poppy, a common flowering plant—are often used. Opiates work by attaching themselves, on the molecular level, to nerve cells normally used to transmit pain messages. (The place on the nerve cells where the opiates reside are called opiate receptors). Opiates work very well in relieving pain, but are quite dangerous and can become addictive.

In the 1970s, scientists began looking for natural opiate-like substances, and found that the body does indeed produce its own painkillers, which has come to be called opioids. The two most common opioids are endorphins and enkephalins. These chemicals attach themselves to the opiate receptors in nerve cells just as opiates do. It has been found that the body can be stimulated to release these chemicals by TENS and by acupuncture, a Chinese method of placing tiny needles at specific points in the body to relieve pain. Other methods for treating pain include hypnotism, massage, and biofeedback .

Further Reading

Arnold, Caroline. Pain: What Is It? How Do We Deal With It?New York: William Morrow and Company, 1986.

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Pain

PAIN

The term "pain" refers to a physical sensation or a distress linked to instinctual tension, which the psychic apparatus then seeks to discharge by work according to the principle of pleasure/unpleasure.

Jean-Bertrand Pontalis (1981) noted that the outline for an original theory of pain can be found in Freud's work from "A Project for a Scientific Psychology" (1950c [1895]) onward. Taken up again in Inhibitions, Symptoms, and Anxiety (1926d [1925]), this theory covers the basic reference points of analytic theory: the theory of narcissism, the question of trauma, the definition of primary masochism, and the presentation of the death instinct. Finally, with the concept of negative therapeutic reaction in place, Freud, in The Ego and the Id (1923b), described how pain drives resistance to analysis, indeed, how pain is the final refuge from renouncing the lost object, as the resistance implies.

By 1895 Freud had postulated bipolarity as the principle of psychic functioning, and, anticipating his later theory of instinctual dualism, he opposed the experience of pain to the experience of satisfaction. In qualitative terms, pain is different from unpleasure in that pain is situated outside the economic apparatus of pleasure/unpleasure. In dynamic terms, "[p]ain is . . . characterized as an irruption of excessively large Qs [quantities] into N [neurones that don't retain quantities of energy] and R [neurones that do retain energy and are capable of retaining memory" (1950c, p. 307). Then the body discharges the accumulated excitation. Pain can cause the subject to break out of preestablished paths only because there are boundaries (bodily boundaries, ego boundaries); however, its internal discharge has an implosive effect. Like a physical or psychic hole (to be distinguished from a possible lacuna or a lack), the excess of excitation caused by pain obstructs all binding activity. Pontalis (1981) has stressed that this theory of pain breaching is a departure from the economic apparatus where the theory of anxiety is more generally situated.

In 1926, in addendum C to Inhibitions, Symptoms and Anxiety, Freud again tried to differentiate pain from anxiety, though not without difficulty or contradiction. Pain is primarily a reaction to the loss of the object, whereas anxiety is a reaction to the danger that loss entails. Pain is the consequence of a breaching of the protective shield, and by acting as a constant instinctual excitation (some authors have proposed the idea of a pseudo-instinct here), it prevents the subject from escaping from it. Nonetheless, pain has a locus: it emanates from the periphery of the body or the organs. If anxiety has already led the subject to regard the loss of the object metaphorically, the unmediated reality of pain ensures that the subject can survive without the loss of the object or the nostalgia of that loss. In a third stage of his exposition in addendum C, Freud returns to the difference between mental pain and physical pain, arguing that the former is much more closely related to the mechanism of anxiety. "The transition from physical pain to mental pain corresponds to a change from narcissistic cathexis to object-cathexis. An object-presentation which is highly cathected by instinctual need plays the same role as a part of the body which is cathected by an increase of stimulus" (1926d, pp. 171-172).

Freud thus uses the same model to describe both physical pain and psychic pain. As Pontalis has made clear, pain is not a case of metaphor but rather a case of analogy—a direct exchange between one level and
another, as if with pain the body mutates into psyche and the psyche into body. But while anxiety can be communicated, pain cannot. Despite a scream of pain, the cry does nothing to ease it. The experience of pain takes place within a bodily ego. Both physical pain and mental pain partake of the content-container relationship (Enriquez, 1980; McDougall, 1978). The subject in pain finds it impossible to recover the object by means of representation: "Where there is pain, it is the lost, absent object that is present; the real, present object that is absent." The distinctive feature of pain is its blurring of boundaries. Thus, for example, certain types of physical suffering serve to alleviate mental pain. Recent clinical work on somatization and borderline states is often faced with this inchoate nature of pain: absolute, naked pain.

Pontalis, Jean-Bertrand. (1981). Frontiers in psychoanalysis: Between the dream and psychic pain (Catherine Cullen and Philip Cullen, Trans.). London: Hogarth Press and the Institute of Psycho-Analysis. (Original work published 1977)

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Pain

Biology
COPYRIGHT 2002 The Gale Group Inc.

Pain

Pain is experienced by humans and animals in response to excessive pressure, heat, or chemicals. Although humans often view pain as undesirable, pain helps protect them from injury by alerting them to its presence. The need for pain is revealed by diseases in which pain is absent or suppressed, as in leprosy. People with such disorders, unaware of injuries or infections, often die prematurely or require limb amputations because unfelt injuries may be neglected until they lead to massive infection and tissue death.

Although skin and other tissues contain cells that are activated by heat and pressure, pain arises from specialized cells that only respond to excessive stimuli that have the potential to cause damage. Light pressure or warming has no effect on these cells. Once activated, these cells transmit pain signals to the spinal cord and brain where pain sensations occur.

Unlike other senses such as sight, pain is highly variable. For example, pain sensitivity decreases in animals pursued or caught by predators, in
women giving birth, and in patients taking pain-killing drugs like morphine. Although the ability of morphine to decrease pain sensation has been known for thousands of years, it was not until the 1970s that specific receptors were found in the brain that mediate the effect of the drug. Shortly thereafter, it was discovered that the human body manufactures its own morphinelike chemicals, known as endorphins, that provide the body with its own builtin pain-regulatory system. This internal pain-suppression system is activated during stress such as fleeing lions or delivering babies.

Injury to skin or nerves can also cause a long-lasting increase in pain sensitivity, known as hyperalgesia, that can persist for days or even years. Sunburn is a common example; the skin burn causes normally nonpainful touch to become painful for days. Changes in both the skin and the central nervous system appear responsible for hyperalgesia. In the skin, chemicals released by inflammation, the process that also causes redness and swelling, sensitize the pain nerve endings to touch. In the central nervous system, neural circuits are permanently altered in much the same way that memories are stored.

Pain arises not only from skin and muscle, but also from internal organs such as the heart and kidney. Interestingly, pain from internal organs is often not perceived as arising from the internal organ, but instead from nearby areas of skin or muscle. This is known as referred pain. For example, heart attacks commonly produce pain perceived to arise from the left shoulder and not the heart.

Neurological injury following trauma or caused by diseases such as diabetes sometimes leads to severe, unrelenting pain. Following amputation, the cut nerve in the limb continues to send pain signals to the brain even though the limb has been severed. Consequently, the brain perceives the pain as arising from the amputated limb. This is known as phantom pain.

Given how commonly humans experience pain, it is not surprising that many medical treatments have been developed to suppress it. For example, aspirin blocks the inflammation in skin that leads to hyperalgesia. Acupuncture, an ancient treatment in which the skin is punctured by a pattern of fine needles, activates the internal morphine system and reduces pain in much the same way as taking morphine.

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pain

The Columbia Encyclopedia, 6th ed.

Copyright The Columbia University Press

pain, unpleasant or hurtful sensation resulting from stimulation of nerve endings. The stimulus is carried by nerve fibers to the spinal cord and then to the brain, where the nerve impulse is interpreted as pain. The excessive stimulation of nerve endings during pain is attributed to tissue damage, and in this sense pain has protective value, serving as a danger signal of disease and often facilitating diagnosis. Unlike other sensory experiences, e.g., response to touch or cold, pain may be modified by sedatives and nonsteroidal anti-inflammatory drugs or, if unusually severe, by opioid narcotics. Recently, patient-controlled analgesic techniques have been introduced, in which patients have the option of injecting small quantities of narcotic type analgesics to control their own pain. Microprocessor-controlled injections may be made through intravenous catheters, or through a catheter into the epidural (covering of the spinal cord) area. If such treatments do not suffice and if the cause of the pain cannot be removed or treated, severing a nerve in the pain pathway may bring relief.

Pain is occasionally felt not only at the site of stimulation but in other parts of the body supplied by nerves in the same sensory path; for example, the pain of angina pectoris or coronary thrombosis may extend to the left arm. This phenomenon is known as referred pain. Subjective or hysterical pain originates in the sensory centers of the brain without stimulation of the nerves at the site of the pain.

Progress has been made in the management of chronic pain and in the education of patients and physicians in such techniques as biofeedback, acupuncture, and meditation and the appropriate use of narcotics and other medications. Using advanced medical-imaging technology, researchers have now located multiple pain centers in the cerebral cortex of the brain, offering promise of possible improvements in measuring and managing pain.

See F. T. Vertosick, Jr., Why We Hurt: The Natural History of Pain (2000).

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pain

pain
/ pān/
•
n.
1.
physical suffering or discomfort caused by illness or injury:
she's in great painthose who suffer from back pain. ∎
a feeling of marked discomfort in a particular part of the body:
he had severe pains in his stomach |
chest pains. ∎
mental suffering or distress:
the pain of loss. ∎
(also pain in the neck or vulgar slang pain in the ass) [in sing.] inf.
an annoying or tedious person or thing:
she's a pain.2. (pains)
careful effort; great care or trouble:
she took pains to see that everyone ate wellhe is at pains to point out that he isn't like that.•
v. [tr.]
cause mental or physical pain to:
it pains me to say thisher legs had been paining her. ∎ [intr.]
(of a part of the body) hurt:
sometimes my right hand would pain.PHRASES:for one's pains inf.
as an unfairly bad return for efforts or trouble:
he was sued for his pains.no pain, no gain
suffering is necessary in order to achieve something.
on
(or under) pain of
the penalty for disobedience or shortcoming being:
all persons are commanded to keep silent on pain of imprisonment.ORIGIN:Middle English (in the sense ‘suffering inflicted as punishment for an offense’): from Old French peine, from Latin poena ‘penalty,’ later ‘pain.’

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pain

pain (payn) n. an unpleasant sensation ranging from mild discomfort to agonized distress, associated with real or potential tissue damage. Pain is a subjective response to impulses from the peripheral nerves in damaged tissue, which pass to nerves in the spinal cord, where they are subjected to a gate control. This gate modifies the subsequent passage of the impulses in accordance with descending controls from the brain. Because attention is a crucial component of pain, distraction can act as a basis for pain therapy. On the other hand, anxiety and depression focus the attention and exaggerate the pain. If the nerve pathways are damaged, the brain can increase the amplification in the pathway, maintaining the sensation as a protective mechanism.

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pain

pain Unpleasant sensation signalling actual or threatened tissue damage as a result of illness or injury; it can be acute (severe but short-lived) or chronic (persisting for a long time). Pain is felt when specific nerve endings are stimulated. Pain is treated in a number of ways, most commonly by drugs known as analgesics.

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Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

Notes:

Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.

In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

Notes:

Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.

In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

Notes:

Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.

In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.